Sending Shared Calendar Invitation using Exchanged Managed API occurs error "null frontEndLocator".
As mentioned in the title, when I send a shared calendar invitation using the Exchange Managed API, I get the error "Value cannot be null. Parameter name: frontEndLocator". Below is the full source code I used. private static void EwsCalendarApi2() { string senderUserId = "Email address removed"; string senderUserPassword = "sharingUserPassword"; string sharedToUser = "Email address removed"; ExchangeService service = new ExchangeService(ExchangeVersion.Exchange2013_SP1); service.Url = new Uri("https://mail.domain.com/EWS/Exchange.asmx"); service.UseDefaultCredentials = false; var cred = new System.Net.NetworkCredential(senderUserId, senderUserPassword); service.Credentials = cred; Guid binSharingProviderGuid = new Guid("{AEF00600-0000-0000-C000-000000000046}"); byte[] byteSharingProviderGuid = binSharingProviderGuid.ToByteArray(); string sharedUserDn = GetMailboxDN(senderUserId, cred); byte[] binInitiatorEntryId = HexStringToByteArray(GetIntiatorEntryID(sharedUserDn)); EmailMessage invitationRequest = new EmailMessage(service); invitationRequest.Subject = "I'd like to share my calendar with you"; invitationRequest.Body = "Sent by Exchange Administrator on behalf of user"; invitationRequest.Sensitivity = Sensitivity.Normal; invitationRequest.ItemClass = "IPM.Sharing"; /* Constant Required Value [MS-ProtocolSpec] */ invitationRequest.SetExtendedProperty(PidTagMessageClass, "IPM.Sharing"); invitationRequest.SetExtendedProperty(PidNameContentClass, "Sharing"); //PidTagNormalizedSubject //PidTagSubjectPrefix invitationRequest.SetExtendedProperty(PidLidSharingProviderGuid, byteSharingProviderGuid);//binary invitationRequest.SetExtendedProperty(PidNameXSharingProviderGuid, "AEF0060000000000C000000000000046"); invitationRequest.SetExtendedProperty(PidLidSharingProviderName, "Microsoft Exchange"); invitationRequest.SetExtendedProperty(PidNameXSharingProviderName, "Microsoft Exchange"); invitationRequest.SetExtendedProperty(PidLidSharingProviderUrl, "http://www.microsoft.com/exchange"); invitationRequest.SetExtendedProperty(PidNameXSharingProviderUrl, "http://www.microsoft.com/exchange"); //invitationRequest.SetExtendedProperty(PidLidSharingConfigurationUrl, ""); //invitationRequest.SetExtendedProperty(PidNameXSharingConfigUrl, ""); invitationRequest.SetExtendedProperty(PidLidSharingFlavor, 0x00020500); invitationRequest.SetExtendedProperty(PidNameXSharingFlavor, "20500"); invitationRequest.SetExtendedProperty(PidLidSharingCapabilities, 0x00040290); invitationRequest.SetExtendedProperty(PidNameXSharingCapabilities, "40290"); invitationRequest.SetExtendedProperty(PiLidSharingLocalType, "IPF.Appointment"); invitationRequest.SetExtendedProperty(PidNameXSharingLocalType, "IPF.Appointment"); invitationRequest.SetExtendedProperty(PidLidSharingInitiatorEntryId, binInitiatorEntryId);//binary invitationRequest.SetExtendedProperty(PidLidSharingInitiatorName, senderUserId.Split('@')[0]);//username invitationRequest.SetExtendedProperty(PidLidSharingInitiatorSmtp, senderUserId);//user emailaddress string invitationMailboxID = GetInvitationMailboxId(service, "exch01", sharedUserDn); CalendarFolder folder = Microsoft.Exchange.WebServices.Data.CalendarFolder.Bind(service, WellKnownFolderName.Calendar); string idForPowerShell = GetConvertedEWSIDinHex(service, folder.Id.UniqueId, senderUserId); CreateSharingMessageAttachment(idForPowerShell, senderUserId, GetIntiatorEntryID(sharedUserDn), invitationMailboxID, sharedToUser, "calendar"); // Add a file attachment by using a stream // We need to do the following in order to prevent 3 extra bytes from being prepended to the attachment string tmpPath = Application.StartupPath + "\\temp\\"; if (!Directory.Exists(tmpPath)) Directory.CreateDirectory(tmpPath); string sharMetadata = File.ReadAllText(tmpPath + "sharing_metadata.xml", Encoding.ASCII); byte[] fileContents; UTF8Encoding encoding = new System.Text.UTF8Encoding(); fileContents = encoding.GetBytes(sharMetadata); // fileContents is a Stream object that represents the content of the file to attach. invitationRequest.Attachments.AddFileAttachment("sharing_metadata.xml", fileContents); // This is where we set those "special" headers and other pertinent // information I noted in Part 1 of this series... Attachment thisAttachment = invitationRequest.Attachments[0]; thisAttachment.ContentType = "application/x-sharing-metadata-xml"; thisAttachment.Name = "sharing_metadata.xml"; thisAttachment.IsInline = false; // Add recipient info and send message invitationRequest.ToRecipients.Add(sharedToUser); invitationRequest.SendAndSaveCopy(); } static String GetConvertedEWSIDinHex(ExchangeService esb, String sID, String strSMTPAdd) { // Create a request to convert identifiers. AlternateId objAltID = new AlternateId(); objAltID.Format = IdFormat.EwsId; objAltID.Mailbox = strSMTPAdd; objAltID.UniqueId = sID; //Convert PR_ENTRYID identifier format to an EWS identifier. AlternateIdBase objAltIDBase = esb.ConvertId(objAltID, IdFormat.HexEntryId); AlternateId objAltIDResp = (AlternateId)objAltIDBase; return objAltIDResp.UniqueId.ToString(); } public static String GetInvitationMailboxId(ExchangeService service, string mailBoxServer, string sharedUserLegacyDn) { //ExchangeService service = new ExchangeService(ExchangeVersion.Exchange2013); //service.ImpersonatedUserId = new ImpersonatedUserId(ConnectingIdType.SmtpAddress, "Email address removed"); // Generate The Store Entry Id for the impersonated user StringBuilder MailboxIDPointer = new StringBuilder(); string fqdn = mailBoxServer; string legacyDN = sharedUserLegacyDn; MailboxIDPointer.Append("00000000"); /* Flags */ MailboxIDPointer.Append("38A1BB1005E5101AA1BB08002B2A56C2"); /* ProviderUID */ MailboxIDPointer.Append("00"); /* Version */ MailboxIDPointer.Append("00"); /* Flag */ MailboxIDPointer.Append("454D534D44422E444C4C00000000"); /* DLLFileName */ MailboxIDPointer.Append("00000000"); /* Wrapped Flags */ MailboxIDPointer.Append("1B55FA20AA6611CD9BC800AA002FC45A"); /* WrappedProvider UID (Mailbox Store Object) */ MailboxIDPointer.Append("0C000000"); /* Wrapped Type (Mailbox Store) */ MailboxIDPointer.Append(ConvertStringToHex(fqdn)); /* ServerShortname (FQDN) */ MailboxIDPointer.Append("00"); /* termination bit */ MailboxIDPointer.Append(ConvertStringToHex(legacyDN)); /* Returns the userDN of the impersonated user */ MailboxIDPointer.Append("00"); /* terminator bit */ //service.ImpersonatedUserId = null; return MailboxIDPointer.ToString(); } public static void CreateSharingMessageAttachment(string folderid, string userSharing, string userSharingEntryID, string invitationMailboxID, string userSharedTo, string dataType) { XmlDocument sharedMetadataXML = new XmlDocument(); try { // just logging stuff as well during my debugging using (StreamWriter w = new StreamWriter("SharingMessageMetaData.txt", false, Encoding.ASCII)) { // Create a String that contains our new sharing_metadata.xml file StringBuilder metadataString = new StringBuilder("<?xml version=\"1.0\"?>"); metadataString.Append("<SharingMessage xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" "); metadataString.Append("xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\" "); metadataString.Append("xmlns=\"http://schemas.microsoft.com/sharing/2008\">"); metadataString.Append("<DataType>" + dataType + "</DataType>"); metadataString.Append("<Initiator>"); metadataString.Append("<Name>" + userSharing.Split('@')[0] + "</Name>"); metadataString.Append("<SmtpAddress>" + userSharing + "</SmtpAddress><EntryId>" + userSharingEntryID.Trim()); metadataString.Append("</EntryId>"); metadataString.Append("</Initiator>"); metadataString.Append("<Invitation>"); metadataString.Append("<Providers>"); metadataString.Append("<Provider Type=\"ms-exchange-internal\" TargetRecipients=\"" + userSharedTo + "\">"); metadataString.Append("<FolderId xmlns=\"http://schemas.microsoft.com/exchange/sharing/2008\">"); metadataString.Append(folderid); metadataString.Append("</FolderId>"); metadataString.Append("<MailboxId xmlns=\"http://schemas.microsoft.com/exchange/sharing/2008\">"); metadataString.Append(invitationMailboxID); metadataString.Append("</MailboxId>"); metadataString.Append("</Provider>"); metadataString.Append("</Providers>"); metadataString.Append("</Invitation>"); metadataString.Append("</SharingMessage>"); // MessageBox.Show(metadataString.ToString(), "metadataString before loading into soapEnvelope"); sharedMetadataXML.LoadXml(metadataString.ToString()); Console.WriteLine($"{0}, {1}, {2}", metadataString.ToString(), w, "Generate XML"); // MessageBox.Show("returning SOAP envelope now"); w.Close(); } string tmpPath = Application.StartupPath + "\\temp\\"; if (!Directory.Exists(tmpPath)) Directory.CreateDirectory(tmpPath); sharedMetadataXML.Save(tmpPath + "sharing_metadata.xml"); } catch (Exception eg) { MessageBox.Show("Exception:" + eg.Message.ToString(), "Error Try CreateSharedMessageInvitation()"); } } static bool RedirectionUrlValidationCallback(String redirectionUrl) { bool redirectionValidated = false; if (redirectionUrl.Equals("https://mail.domain.com/autodiscover/autodiscover.xml")) { redirectionValidated = true; } return redirectionValidated; } public static String GetMailboxDN(string senderUserId, System.Net.NetworkCredential cred) { string result = "error"; AutodiscoverService autodiscoverService = new AutodiscoverService(); // The following RedirectionUrlValidationCallback required for httpsredirection. autodiscoverService.RedirectionUrlValidationCallback = RedirectionUrlValidationCallback; autodiscoverService.Credentials = cred; // Get the user settings. // Submit a request and get the settings. The response contains only the // settings that are requested, if they exist. GetUserSettingsResponse userresponse = autodiscoverService.GetUserSettings( senderUserId.ToString(), UserSettingName.UserDisplayName, UserSettingName.UserDN ); foreach (var usersetting in userresponse.Settings) { if (usersetting.Key.ToString() == "UserDN") { result = usersetting.Value.ToString(); } } return result; } static string GetIntiatorEntryID(string legacyDN) { String result = String.Empty; //// Bind to EWS //ExchangeService service = ExchangeConnection.ExchangeService(); //service.ImpersonatedUserId = //new ImpersonatedUserId(ConnectingIdType.SmtpAddress, senderUserId); //// Get LegacyDN Using the function above this one //string legacyDNinHex = ConvertStringToHex(sharedByLegacyDN); string legacyDNinHex = ConvertStringToHex(legacyDN); StringBuilder addBookEntryId = new StringBuilder(); addBookEntryId.Append("00000000"); /* Flags */ addBookEntryId.Append("DCA740C8C042101AB4B908002B2FE182"); /* ProviderUID */ addBookEntryId.Append("01000000"); /* Version */ addBookEntryId.Append("00000000"); /* Type - 00 00 00 00 = Local Mail User */ addBookEntryId.Append(legacyDNinHex); /* Returns the userDN of the impersonated user */ addBookEntryId.Append("00"); /* terminator bit */ result = addBookEntryId.ToString(); //service.ImpersonatedUserId = null; return result; } static string ConvertStringToHex(string input) { // Take our input and break it into an array char[] arrInput = input.ToCharArray(); String result = String.Empty; // For each set of characters foreach (char element in arrInput) { if (String.IsNullOrEmpty(result)) { result = String.Format("{0:X2}", Convert.ToUInt16(element)).ToString(); } else { result += String.Format("{0:X2}", Convert.ToUInt16(element)).ToString(); } } return result.ToString(); } static byte[] HexStringToByteArray(string input) { byte[] Bytes; int ByteLength; string HexValue = "\x0\x1\x2\x3\x4\x5\x6\x7\x8\x9|||||||\xA\xB\xC\xD\xE\xF"; ByteLength = input.Length / 2; Bytes = new byte[ByteLength]; for (int x = 0, i = 0; i < input.Length; i += 2, x += 1) { Bytes[x] = (byte)(HexValue[Char.ToUpper(input[i + 0]) - '0'] << 4); Bytes[x] |= (byte)(HexValue[Char.ToUpper(input[i + 1]) - '0']); } return Bytes; } static ExtendedPropertyDefinition PidTagMessageClass = new ExtendedPropertyDefinition(0x001A, MapiPropertyType.String); static ExtendedPropertyDefinition PidNameContentClass = new ExtendedPropertyDefinition(new Guid("{00020386-0000-0000-c000-000000000046}"), "Content-Class", MapiPropertyType.String); static ExtendedPropertyDefinition PidLidSharingProviderGuid = new ExtendedPropertyDefinition(new Guid("{00062040-0000-0000-C000-000000000046}"), "0x00008A01", MapiPropertyType.Binary); static ExtendedPropertyDefinition PidNameXSharingProviderGuid = new ExtendedPropertyDefinition(new Guid("{00020386-0000-0000-C000-000000000046}"), "X-Sharing-Provider-Guid", MapiPropertyType.String); static ExtendedPropertyDefinition PidLidSharingProviderName = new ExtendedPropertyDefinition(new Guid("{00062040-0000-0000-C000-000000000046}"), "0x00008A02", MapiPropertyType.String); static ExtendedPropertyDefinition PidNameXSharingProviderName = new ExtendedPropertyDefinition(new Guid("{00020386-0000-0000-C000-000000000046}"), "X-Sharing-Provider-Name", MapiPropertyType.String); static ExtendedPropertyDefinition PidLidSharingProviderUrl = new ExtendedPropertyDefinition(new Guid("{00062040-0000-0000-C000-000000000046}"), "0x00008A03", MapiPropertyType.String); static ExtendedPropertyDefinition PidNameXSharingProviderUrl = new ExtendedPropertyDefinition(new Guid("{00020386-0000-0000-C000-000000000046}"), "X-Sharing-Provider-Url", MapiPropertyType.String); static ExtendedPropertyDefinition PidLidSharingConfigurationUrl = new ExtendedPropertyDefinition(new Guid("{00062040-0000-0000-C000-000000000046}"), "0x00008A24", MapiPropertyType.String); static ExtendedPropertyDefinition PidNameXSharingConfigUrl = new ExtendedPropertyDefinition(new Guid("{00020386-0000-0000-C000-000000000046}"), "X-Sharing-Config-Url", MapiPropertyType.String); static ExtendedPropertyDefinition PidLidSharingFlavor = new ExtendedPropertyDefinition(new Guid("{00062040-0000-0000-C000-000000000046}"), "0x00008A18", MapiPropertyType.Integer); static ExtendedPropertyDefinition PidNameXSharingFlavor = new ExtendedPropertyDefinition(new Guid("{00020386-0000-0000-C000-000000000046}"), "X-Sharing-Flavor", MapiPropertyType.String); static ExtendedPropertyDefinition PidLidSharingCapabilities = new ExtendedPropertyDefinition(new Guid("{00062040-0000-0000-C000-000000000046}"), "0x00008A17", MapiPropertyType.Integer); static ExtendedPropertyDefinition PidNameXSharingCapabilities = new ExtendedPropertyDefinition(new Guid("{00020386-0000-0000-C000-000000000046}"), "X-Sharing-Capabilities", MapiPropertyType.String); static ExtendedPropertyDefinition PiLidSharingLocalType = new ExtendedPropertyDefinition(new Guid("{00062040-0000-0000-C000-000000000046}"), "0x00008A14", MapiPropertyType.String); static ExtendedPropertyDefinition PidNameXSharingLocalType = new ExtendedPropertyDefinition(new Guid("{00020386-0000-0000-C000-000000000046}"), "X-Sharing-Local-Type", MapiPropertyType.String); static ExtendedPropertyDefinition PidLidSharingInitiatorEntryId = new ExtendedPropertyDefinition(new Guid("{00062040-0000-0000-C000-000000000046}"), "0x00008A09", MapiPropertyType.Binary); static ExtendedPropertyDefinition PidLidSharingInitiatorName = new ExtendedPropertyDefinition(new Guid("{00062040-0000-0000-C000-000000000046}"), "0x00008A07", MapiPropertyType.String); static ExtendedPropertyDefinition PidLidSharingInitiatorSmtp = new ExtendedPropertyDefinition(new Guid("{00062040-0000-0000-C000-000000000046}"), "0x00008A08", MapiPropertyType.String); static ExtendedPropertyDefinition PidLidSharingRemoteName = new ExtendedPropertyDefinition(new Guid("{00062040-0000-0000-C000-000000000046}"), "0x00008A05", MapiPropertyType.String); static ExtendedPropertyDefinition PidNameXSharingRemoteName = new ExtendedPropertyDefinition(new Guid("{00020386-0000-0000-C000-000000000046}"), "X-Sharing-Remote-Name", MapiPropertyType.String); static ExtendedPropertyDefinition PidLidSharingRemoteType = new ExtendedPropertyDefinition(new Guid("{00062040-0000-0000-C000-000000000046}"), "0x00008A1D", MapiPropertyType.String); static ExtendedPropertyDefinition PidNameXSharingRemoteType = new ExtendedPropertyDefinition(new Guid("{00020386-0000-0000-C000-000000000046}"), "X-Sharing-Remote-Type", MapiPropertyType.String); static ExtendedPropertyDefinition PidLidSharingRemoteUid = new ExtendedPropertyDefinition(new Guid("{00062040-0000-0000-C000-000000000046}"), "0x00008A06", MapiPropertyType.String); static ExtendedPropertyDefinition PidNameXSharingRemoteUid = new ExtendedPropertyDefinition(new Guid("{00020386-0000-0000-C000-000000000046}"), "X-Sharing-Remote-Uid", MapiPropertyType.String); static ExtendedPropertyDefinition PidLidSharingRemoteStoreUid = new ExtendedPropertyDefinition(new Guid("{00062040-0000-0000-C000-000000000046}"), "0x00008A48", MapiPropertyType.String); static ExtendedPropertyDefinition PidNameXSharingRemoteStoreUid = new ExtendedPropertyDefinition(new Guid("{00020386-0000-0000-C000-000000000046}"), "X-Sharing-Remote-Store-Uid", MapiPropertyType.String); static ExtendedPropertyDefinition PidLidSharingResponseType = new ExtendedPropertyDefinition(new Guid("{00062040-0000-0000-C000-000000000046}"), "0x00008A27", MapiPropertyType.String); static ExtendedPropertyDefinition PidLidSharingResponseTime = new ExtendedPropertyDefinition(new Guid("{00062040-0000-0000-C000-000000000046}"), "0x00008A28", MapiPropertyType.String); And errors. ServiceDiagnostics_SendWatsonReportOnUnhandledException=System.ArgumentNullException: Value cannot be null. Parameter name: frontEndLocator Microsoft.Exchange.Data.Storage.SharingProviderHandler.PerformInvitation(MailboxSession mailboxSession SharingContext context ValidRecipient[] recipients IFrontEndLocator frontEndLocator Boolean isUpdateOfPermission) Microsoft.Exchange.Data.Storage.SharingMessageItem.PerformInvitation(Boolean isUpdateOfPermission) Microsoft.Exchange.Data.Storage.SharingMessageItem.OnBeforeSend() Microsoft.Exchange.Data.Storage.CoreItem.<OnBeforeSend>b__113_0() Microsoft.Exchange.Data.Storage.CoreItem.<>c__DisplayClass76_0.<Submit>b__0() Microsoft.Exchange.Data.Storage.MessageItem.InternalSend(StoreObjectId saveSentMessageFolder SubmitMessageFlags submitFlags Boolean doNotMove Boolean shouldSkipPDLMembersWithoutSMTP) Microsoft.Exchange.Data.Storage.MessageItem.Send(StoreObjectId saveSentMessageFolder SubmitMessageFlags submitFlags Boolean doNotMove SaveMode saveMode Boolean shouldSkipPDLMembersWithoutSMTP) Microsoft.Exchange.Services.Core.SendItem.SendItemById(IdAndSession sendIdAndSession IdAndSession folderIdAndSessionToSaveIn) Microsoft.Exchange.Services.Core.SendItem.Execute() Microsoft.Exchange.Services.Core.ExceptionHandler`1.Execute(IRequestDetailsLogger logger CreateServiceResult createServiceResult Int32 index ExecutionOption executionOption) Microsoft.Exchange.Services.Core.BaseStepServiceCommand`3.InternalExecuteStep(Boolean& isBatchStopResponse) Microsoft.Exchange.Services.Core.ServiceCommandBase`1.<ExecuteStep>b__82_0() Microsoft.Exchange.Services.Core.ServiceCommandBase`1.<>c__DisplayClass88_0.<ExecuteHelper>b__0() Microsoft.Exchange.Common.IL.ILUtil.DoTryFilterCatch(Action tryDelegate Func`2 filterDelegate Action`1 catchDelegate);BaseServiceTask_SendWatsonReportOnGrayException=Microsoft.Exchange.Common.GrayException ---> System.ArgumentNullException: Value cannot be null. Parameter name: frontEndLocator Microsoft.Exchange.Data.Storage.SharingProviderHandler.PerformInvitation(MailboxSession mailboxSession SharingContext context ValidRecipient[] recipients IFrontEndLocator frontEndLocator Boolean isUpdateOfPermission) Microsoft.Exchange.Data.Storage.SharingMessageItem.PerformInvitation(Boolean isUpdateOfPermission) Microsoft.Exchange.Data.Storage.SharingMessageItem.OnBeforeSend() Microsoft.Exchange.Data.Storage.CoreItem.<OnBeforeSend>b__113_0() Microsoft.Exchange.Data.Storage.CoreItem.<>c__DisplayClass76_0.<Submit>b__0() Microsoft.Exchange.Data.Storage.MessageItem.InternalSend(StoreObjectId saveSentMessageFolder SubmitMessageFlags submitFlags Boolean doNotMove Boolean shouldSkipPDLMembersWithoutSMTP) Microsoft.Exchange.Data.Storage.MessageItem.Send(StoreObjectId saveSentMessageFolder SubmitMessageFlags submitFlags Boolean doNotMove SaveMode saveMode Boolean shouldSkipPDLMembersWithoutSMTP) Microsoft.Exchange.Services.Core.SendItem.SendItemById(IdAndSession sendIdAndSession IdAndSession folderIdAndSessionToSaveIn) Microsoft.Exchange.Services.Core.SendItem.Execute() Microsoft.Exchange.Services.Core.ExceptionHandler`1.Execute(IRequestDetailsLogger logger CreateServiceResult createServiceResult Int32 index ExecutionOption executionOption) Microsoft.Exchange.Services.Core.BaseStepServiceCommand`3.InternalExecuteStep(Boolean& isBatchStopResponse) Microsoft.Exchange.Services.Core.ServiceCommandBase`1.<ExecuteStep>b__82_0() Microsoft.Exchange.Services.Core.ServiceCommandBase`1.<>c__DisplayClass88_0.<ExecuteHelper>b__0() Microsoft.Exchange.Common.IL.ILUtil.DoTryFilterCatch(Action tryDelegate Func`2 filterDelegate Action`1 catchDelegate) Microsoft.Exchange.Services.Core.ServiceDiagnostics.SendWatsonReportOnUnhandledException(ICallContext callContext Action methodDelegate) Microsoft.Exchange.Services.Core.ServiceCommandBase`1.ExecuteHelper(Func`1 action) Microsoft.Exchange.Services.Core.Types.ServiceTask`1.<>c__DisplayClass11_0.<ExecuteHelper>b__0() Microsoft.Exchange.Common.IL.ILUtil.DoTryFilterCatch(Action tryDelegate Func`2 filterDelegate Action`1 catchDelegate) --- End of inner exception stack trace --- Microsoft.Exchange.Common.GrayException.ExceptionCatcher(Object exception) Microsoft.Exchange.Common.IL.ILUtil.DoTryFilterCatch(Action tryDelegate Func`2 filterDelegate Action`1 catchDelegate) Microsoft.Exchange.Services.Core.Types.BaseServiceTask`1.SendWatsonReportOnGrayException(Action callback Action exceptionHandlerCallback Boolean isGrayExceptionTaskFailure);BaseServiceTask_FinishRequest=Microsoft.Exchange.Common.GrayException ---> System.ArgumentNullException: Value cannot be null. Parameter name: frontEndLocator Microsoft.Exchange.Data.Storage.SharingProviderHandler.PerformInvitation(MailboxSession mailboxSession SharingContext context ValidRecipient[] recipients IFrontEndLocator frontEndLocator Boolean isUpdateOfPermission) Microsoft.Exchange.Data.Storage.SharingMessageItem.PerformInvitation(Boolean isUpdateOfPermission) Microsoft.Exchange.Data.Storage.SharingMessageItem.OnBeforeSend() Microsoft.Exchange.Data.Storage.CoreItem.<OnBeforeSend>b__113_0() Microsoft.Exchange.Data.Storage.CoreItem.<>c__DisplayClass76_0.<Submit>b__0() Microsoft.Exchange.Data.Storage.MessageItem.InternalSend(StoreObjectId saveSentMessageFolder SubmitMessageFlags submitFlags Boolean doNotMove Boolean shouldSkipPDLMembersWithoutSMTP) Microsoft.Exchange.Data.Storage.MessageItem.Send(StoreObjectId saveSentMessageFolder SubmitMessageFlags submitFlags Boolean doNotMove SaveMode saveMode Boolean shouldSkipPDLMembersWithoutSMTP) Microsoft.Exchange.Services.Core.SendItem.SendItemById(IdAndSession sendIdAndSession IdAndSession folderIdAndSessionToSaveIn) Microsoft.Exchange.Services.Core.SendItem.Execute() Microsoft.Exchange.Services.Core.ExceptionHandler`1.Execute(IRequestDetailsLogger logger CreateServiceResult createServiceResult Int32 index ExecutionOption executionOption) Microsoft.Exchange.Services.Core.BaseStepServiceCommand`3.InternalExecuteStep(Boolean& isBatchStopResponse) Microsoft.Exchange.Services.Core.ServiceCommandBase`1.<ExecuteStep>b__82_0() Microsoft.Exchange.Services.Core.ServiceCommandBase`1.<>c__DisplayClass88_0.<ExecuteHelper>b__0() Microsoft.Exchange.Common.IL.ILUtil.DoTryFilterCatch(Action tryDelegate Func`2 filterDelegate Action`1 catchDelegate) Microsoft.Exchange.Services.Core.ServiceDiagnostics.SendWatsonReportOnUnhandledException(ICallContext callContext Action methodDelegate) Microsoft.Exchange.Services.Core.ServiceCommandBase`1.ExecuteHelper(Func`1 action) Microsoft.Exchange.Services.Core.Types.ServiceTask`1.<>c__DisplayClass11_0.<ExecuteHelper>b__0() Microsoft.Exchange.Common.IL.ILUtil.DoTryFilterCatch(Action tryDelegate Func`2 filterDelegate Action`1 catchDelegate) --- End of inner exception stack trace --- Microsoft.Exchange.Common.GrayException.ExceptionCatcher(Object exception) Microsoft.Exchange.Common.IL.ILUtil.DoTryFilterCatch(Action tryDelegate Func`2 filterDelegate Action`1 catchDelegate) Microsoft.Exchange.Services.Core.Types.BaseServiceTask`1.SendWatsonReportOnGrayException(Action callback Action exceptionHandlerCallback Boolean isGrayExceptionTaskFailure);BaseServiceTask_CompleteWCFRequest=Microsoft.Exchange.Common.GrayException ---> System.ArgumentNullException: Value cannot be null. Parameter name: frontEndLocator Microsoft.Exchange.Data.Storage.SharingProviderHandler.PerformInvitation(MailboxSession mailboxSession SharingContext context ValidRecipient[] recipients IFrontEndLocator frontEndLocator Boolean isUpdateOfPermission) Microsoft.Exchange.Data.Storage.SharingMessageItem.PerformInvitation(Boolean isUpdateOfPermission) Microsoft.Exchange.Data.Storage.SharingMessageItem.OnBeforeSend() Microsoft.Exchange.Data.Storage.CoreItem.<OnBeforeSend>b__113_0() Microsoft.Exchange.Data.Storage.CoreItem.<>c__DisplayClass76_0.<Submit>b__0() Microsoft.Exchange.Data.Storage.MessageItem.InternalSend(StoreObjectId saveSentMessageFolder SubmitMessageFlags submitFlags Boolean doNotMove Boolean shouldSkipPDLMembersWithoutSMTP) Microsoft.Exchange.Data.Storage.MessageItem.Send(StoreObjectId saveSentMessageFolder SubmitMessageFlags submitFlags Boolean doNotMove SaveMode saveMode Boolean shouldSkipPDLMembersWithoutSMTP) Microsoft.Exchange.Services.Core.SendItem.SendItemById(IdAndSession sendIdAndSession IdAndSession folderIdAndSessionToSaveIn) Microsoft.Exchange.Services.Core.SendItem.Execute() Microsoft.Exchange.Services.Core.ExceptionHandler`1.Execute(IRequestDetailsLogger logger CreateServiceResult createServiceResult Int32 index ExecutionOption executionOption) Microsoft.Exchange.Services.Core.BaseStepServiceCommand`3.InternalExecuteStep(Boolean& isBatchStopResponse) Microsoft.Exchange.Services.Core.ServiceCommandBase`1.<ExecuteStep>b__82_0() Microsoft.Exchange.Services.Core.ServiceCommandBase`1.<>c__DisplayClass88_0.<ExecuteHelper>b__0() Microsoft.Exchange.Common.IL.ILUtil.DoTryFilterCatch(Action tryDelegate Func`2 filterDelegate Action`1 catchDelegate) Microsoft.Exchange.Services.Core.ServiceDiagnostics.SendWatsonReportOnUnhandledException(ICallContext callContext Action methodDelegate) Microsoft.Exchange.Services.Core.ServiceCommandBase`1.ExecuteHelper(Func`1 action) Microsoft.Exchange.Services.Core.Types.ServiceTask`1.<>c__DisplayClass11_0.<ExecuteHelper>b__0() Microsoft.Exchange.Common.IL.ILUtil.DoTryFilterCatch(Action tryDelegate Func`2 filterDelegate Action`1 catchDelegate) --- End of inner exception stack trace --- Microsoft.Exchange.Common.GrayException.ExceptionCatcher(Object exception) Microsoft.Exchange.Common.IL.ILUtil.DoTryFilterCatch(Action tryDelegate Func`2 filterDelegate Action`1 catchDelegate) Microsoft.Exchange.Services.Core.Types.BaseServiceTask`1.SendWatsonReportOnGrayException(Action callback Action exceptionHandlerCallback Boolean isGrayExceptionTaskFailure);FaultInnerException=Microsoft.Exchange.Services.Core.Types.ErrorInternalServerErrorException: An internal server error occurred. The operation failed. ---> System.ArgumentNullException: Value cannot be null. Parameter name: frontEndLocator Microsoft.Exchange.Data.Storage.SharingProviderHandler.PerformInvitation(MailboxSession mailboxSession SharingContext context ValidRecipient[] recipients IFrontEndLocator frontEndLocator Boolean isUpdateOfPermission) Microsoft.Exchange.Data.Storage.SharingMessageItem.PerformInvitation(Boolean isUpdateOfPermission) Microsoft.Exchange.Data.Storage.SharingMessageItem.OnBeforeSend() Microsoft.Exchange.Data.Storage.CoreItem.<OnBeforeSend>b__113_0() Microsoft.Exchange.Data.Storage.CoreItem.<>c__DisplayClass76_0.<Submit>b__0() Microsoft.Exchange.Data.Storage.MessageItem.InternalSend(StoreObjectId saveSentMessageFolder SubmitMessageFlags submitFlags Boolean doNotMove Boolean shouldSkipPDLMembersWithoutSMTP) Microsoft.Exchange.Data.Storage.MessageItem.Send(StoreObjectId saveSentMessageFolder SubmitMessageFlags submitFlags Boolean doNotMove SaveMode saveMode Boolean shouldSkipPDLMembersWithoutSMTP) Microsoft.Exchange.Services.Core.SendItem.SendItemById(IdAndSession sendIdAndSession IdAndSession folderIdAndSessionToSaveIn) Microsoft.Exchange.Services.Core.SendItem.Execute() Microsoft.Exchange.Services.Core.ExceptionHandler`1.Execute(IRequestDetailsLogger logger CreateServiceResult createServiceResult Int32 index ExecutionOption executionOption) Microsoft.Exchange.Services.Core.BaseStepServiceCommand`3.InternalExecuteStep(Boolean& isBatchStopResponse) Microsoft.Exchange.Services.Core.ServiceCommandBase`1.<ExecuteStep>b__82_0() Microsoft.Exchange.Services.Core.ServiceCommandBase`1.<>c__DisplayClass88_0.<ExecuteHelper>b__0() Microsoft.Exchange.Common.IL.ILUtil.DoTryFilterCatch(Action tryDelegate Func`2 filterDelegate Action`1 catchDelegate) Microsoft.Exchange.Services.Core.ServiceDiagnostics.SendWatsonReportOnUnhandledException(ICallContext callContext Action methodDelegate) Microsoft.Exchange.Services.Core.ServiceCommandBase`1.ExecuteHelper(Func`1 action) Microsoft.Exchange.Services.Core.Types.ServiceTask`1.<>c__DisplayClass11_0.<ExecuteHelper>b__0() Microsoft.Exchange.Common.IL.ILUtil.DoTryFilterCatch(Action tryDelegate Func`2 filterDelegate Action`1 catchDelegate) --- End of inner exception stack trace --- Microsoft.Exchange.Services.Wcf.EWSService.GetServiceAsyncResult[TSoapResponseBody](IAsyncResult result) Microsoft.Exchange.Services.Wcf.EWSService.CreateSoapResponse[TSoapResponse TSoapResponseBody](IAsyncResult result Func`2 createSoapResponseCallback) AsyncInvokeEndEndSendItem(Object Object[] IAsyncResult ) System.ServiceModel.Dispatcher.AsyncMethodInvoker.InvokeEnd(Object instance Object[]& outputs IAsyncResult result) System.ServiceModel.Dispatcher.DispatchOperationRuntime.InvokeEnd(MessageRpc& rpc) System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage7(MessageRpc& rpc) System.ServiceModel.Dispatcher.MessageRpc.Process(Boolean isOperationContextSet);ExceptionHandlerBase_ProvideFault_Error=Microsoft.Exchange.Services.Core.Types.ErrorInternalServerErrorException: An internal server error occurred. The operation failed. ---> System.ArgumentNullException: Value cannot be null. Parameter name: frontEndLocator Microsoft.Exchange.Data.Storage.SharingProviderHandler.PerformInvitation(MailboxSession mailboxSession SharingContext context ValidRecipient[] recipients IFrontEndLocator frontEndLocator Boolean isUpdateOfPermission) Microsoft.Exchange.Data.Storage.SharingMessageItem.PerformInvitation(Boolean isUpdateOfPermission) Microsoft.Exchange.Data.Storage.SharingMessageItem.OnBeforeSend() Microsoft.Exchange.Data.Storage.CoreItem.<OnBeforeSend>b__113_0() Microsoft.Exchange.Data.Storage.CoreItem.<>c__DisplayClass76_0.<Submit>b__0() Microsoft.Exchange.Data.Storage.MessageItem.InternalSend(StoreObjectId saveSentMessageFolder SubmitMessageFlags submitFlags Boolean doNotMove Boolean shouldSkipPDLMembersWithoutSMTP) Microsoft.Exchange.Data.Storage.MessageItem.Send(StoreObjectId saveSentMessageFolder SubmitMessageFlags submitFlags Boolean doNotMove SaveMode saveMode Boolean shouldSkipPDLMembersWithoutSMTP) Microsoft.Exchange.Services.Core.SendItem.SendItemById(IdAndSession sendIdAndSession IdAndSession folderIdAndSessionToSaveIn) Microsoft.Exchange.Services.Core.SendItem.Execute() Microsoft.Exchange.Services.Core.ExceptionHandler`1.Execute(IRequestDetailsLogger logger CreateServiceResult createServiceResult Int32 index ExecutionOption executionOption) Microsoft.Exchange.Services.Core.BaseStepServiceCommand`3.InternalExecuteStep(Boolean& isBatchStopResponse) Microsoft.Exchange.Services.Core.ServiceCommandBase`1.<ExecuteStep>b__82_0() Microsoft.Exchange.Services.Core.ServiceCommandBase`1.<>c__DisplayClass88_0.<ExecuteHelper>b__0() Microsoft.Exchange.Common.IL.ILUtil.DoTryFilterCatch(Action tryDelegate Func`2 filterDelegate Action`1 catchDelegate) Microsoft.Exchange.Services.Core.ServiceDiagnostics.SendWatsonReportOnUnhandledException(ICallContext callContext Action methodDelegate) Microsoft.Exchange.Services.Core.ServiceCommandBase`1.ExecuteHelper(Func`1 action) Microsoft.Exchange.Services.Core.Types.ServiceTask`1.<>c__DisplayClass11_0.<ExecuteHelper>b__0() Microsoft.Exchange.Common.IL.ILUtil.DoTryFilterCatch(Action tryDelegate Func`2 filterDelegate Action`1 catchDelegate) --- End of inner exception stack trace --- Microsoft.Exchange.Services.Wcf.EWSService.GetServiceAsyncResult[TSoapResponseBody](IAsyncResult result) Microsoft.Exchange.Services.Wcf.EWSService.CreateSoapResponse[TSoapResponse TSoapResponseBody](IAsyncResult result Func`2 createSoapResponseCallback) How can I fix this error?