shared mailbox

[Rising Flight]

Hi experts we are using exchange hybrid environment.  i have given Full Access to Cloud user to Onprem shared mailbox.  When cloud user tries to open shared mailbox in outlook he is getting below error

Cannot expand the folder. The set of folders cannot be opened. The file
C:\Users\user1.mydomain.com\AppData\Local\Microsoft\clouduser@mydomain.com.ost is in use and cannot be accessed.
Close any application that is using this file, and then try again.
You might need to restart your computer 

i have used these syntaxes nothing worked for me

Add-MailboxPermission -Identity OnPremSharedMailbox -User clouduser@mydomain.com -AccessRights FullAccess -InheritanceType All
-------------------------------------------------

PS] C:\Windows\system32>Set-ADUser -Identity "OnPremSharedMailbox" -Add @{msExchDelegateListLink="CN=CloudUser,OU=SM,DC=mydomain,DC=com";msExchDelegateListBL = "cloud.user@mydomain.com"}
Set-ADUser : The attribute cannot be modified because it is owned by the system
At line:1 char:1
+ Set-ADUser -Identity "OnPremSharedMailbox" -Add @{msExchDelegateListLink ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo         : NotSpecified: (OnPremSharedMailbox:ADUser) [Set-ADUser], ADException
    + FullyQualifiedErrorId : ActiveDirectoryServer:8369,Microsoft.ActiveDirectory.Management.Commands.SetADUser 

experts please help me i unable to resolve this issue

[#2 · Accepted solution]

Hello!

I have seen this issue before, and for me it was kind of a wonky fix, so I am hoping it is the same for you.

In Office 365, they use what they call Automapping. At its core it is great, as it maps appropriate resources to your users without them having to manage them in outlook. However, if there is some sort of issue (or perhaps access across systems) the automapping can confuse the program to think the file is being access when its not.

So i would first try removing the automapping permissions if they are set. To do that remove any permission that are set already, and then add them back in with the flag -Automapping $false

Secondly I would check to see if you have the "download shared folders" options set in the users account settings (in outlook), which could perhaps cause this behavior. Try removing that setting, and restarting outlook to see if it help.

Not sure if either of these will help, but that is how I fixed my issue. Goodluck, and if not let me know and I can see what else i can find!
adam