Error During Exchange 2013 CU15 Setup

I am trying to install additional exchange server 2013 CU 15 as mailbox server. I face the following error:

Error:
The following error was generated when "$error.Clear();
if (($RoleIsDatacenter -ne $true) -and ($RoleIsDatacenterDedicated -ne $true))
{
if (test-ExchangeServersWriteAccess -DomainController $RoleDomainController -ErrorAction SilentlyContinue)
{
# upgrade the discovery mailboxes to R5 version, this will fix the RecipientDisplayType property of the discovery mailbox which was wrong in R4.
get-mailbox -RecipientTypeDetails DiscoveryMailbox -DomainController $RoleDomainController | where {$_.IsValid -eq $false} | set-mailbox -DomainController $RoleDomainController
$name = [Microsoft.Exchange.Management.RecipientTasks.EnableMailbox]::DiscoveryMailboxUniqueName;
$dispname = [Microsoft.Exchange.Management.RecipientTasks.EnableMailbox]::DiscoveryMailboxDisplayName;
$mbxs = @( get-mailbox -Filter {name -eq $name} -IgnoreDefaultScope -resultSize 1 );
if ( $mbxs.length -eq 0)
{
$dbs = @(get-MailboxDatabase -Server:$RoleFqdnOrName -DomainController $RoleDomainController);
if($dbs.Length -ne 0)
{
$mbxUser = @(get-user -Filter {name -eq $name} -IgnoreDefaultScope -ResultSize 1);
if ($mbxUser.Length -ne 0)
{
enable-mailbox -Discovery -identity $mbxUser[0] -DisplayName $dispname -database $dbs[0].Identity;
}
}
}
}
else
{
write-exchangesetuplog -info "Skipping creating Discovery Search Mailbox because of insufficient permission."
}
}
" was run: "Microsoft.Exchange.Data.DataValidationException: Database is mandatory on UserMailbox.".

Error:
The following error was generated when "$error.Clear();
if (($RoleIsDatacenter -ne $true) -and ($RoleIsDatacenterDedicated -ne $true))
{
if (test-ExchangeServersWriteAccess -DomainController $RoleDomainController -ErrorAction SilentlyContinue)
{
# upgrade the discovery mailboxes to R5 version, this will fix the RecipientDisplayType property of the discovery mailbox which was wrong in R4.
get-mailbox -RecipientTypeDetails DiscoveryMailbox -DomainController $RoleDomainController | where {$_.IsValid -eq $false} | set-mailbox -DomainController $RoleDomainController
$name = [Microsoft.Exchange.Management.RecipientTasks.EnableMailbox]::DiscoveryMailboxUniqueName;
$dispname = [Microsoft.Exchange.Management.RecipientTasks.EnableMailbox]::DiscoveryMailboxDisplayName;
$mbxs = @( get-mailbox -Filter {name -eq $name} -IgnoreDefaultScope -resultSize 1 );
if ( $mbxs.length -eq 0)
{
$dbs = @(get-MailboxDatabase -Server:$RoleFqdnOrName -DomainController $RoleDomainController);
if($dbs.Length -ne 0)
{
$mbxUser = @(get-user -Filter {name -eq $name} -IgnoreDefaultScope -ResultSize 1);
if ($mbxUser.Length -ne 0)
{
enable-mailbox -Discovery -identity $mbxUser[0] -DisplayName $dispname -database $dbs[0].Identity;
}
}
}
}
else
{
write-exchangesetuplog -info "Skipping creating Discovery Search Mailbox because of insufficient permission."
}
}
" was run: "Microsoft.Exchange.Data.DataValidationException: Database is mandatory on UserMailbox.
at Microsoft.Exchange.Configuration.Tasks.Task.ThrowError(Exception exception, ErrorCategory errorCategory, Object target, String helpUrl)
at Microsoft.Exchange.Configuration.Tasks.Task.WriteError(Exception exception, ErrorCategory category, Object target, Boolean reThrow)
at Microsoft.Exchange.Configuration.Tasks.DataAccessTask`1.Validate(TDataObject dataObject)
at Microsoft.Exchange.Configuration.Tasks.SetTaskBase`1.InternalValidate()
at Microsoft.Exchange.Configuration.Tasks.SetRecipientObjectTask`3.InternalValidate()
at Microsoft.Exchange.Management.Common.SetMailEnabledRecipientObjectTask`3.InternalValidate()
at Microsoft.Exchange.Management.RecipientTasks.SetUserBase`2.InternalValidate()
at Microsoft.Exchange.Management.RecipientTasks.SetMailboxBase`2.InternalValidate()
at Microsoft.Exchange.Management.RecipientTasks.SetMailbox.InternalValidate()
at Microsoft.Exchange.Configuration.Tasks.Task.<ProcessRecord>b__b()
at Microsoft.Exchange.Configuration.Tasks.Task.InvokeRetryableFunc(String funcName, Action func, Boolean terminatePipelineIfFailed)".