I worked with one of the client last week, they had one strange issue with all of there Mac 2011 outlook clients.

As per the client Outlook 2011 started getting the prompt since last few days and prior to this they were working fine.

Exchange Server 2007 SP2 with latest Rollup Updates.

We recreated the profile and it worked for around 30 minutes and failed again with the error above error message.
As Outlook and OWA was working fine correctly i didn't thought of that it could be anything else. Moved the mailbox into another Mailbox Database and checked the issue, and guess what it worked fine for another 30 minute and got the same popup again.
If i click on No and reopen the client than it works fine for sometime and give the same error message.
We had total three outlook 2011 clients on Mac and rest of them were using Outlook 2007.

Removed the EWS VirtualDirectory and recreated the EWS VirtualDirectory New-WebServicesVirtualDirectory and the issue got resolved.

Cheers,
-Gulab

First you need to create the .csv file having the alias or Displayname in the format and save it as batch2.csv

Alias
hman
gmal
iqbo

Then we need to run the command from the Exchange Management Shell.

"Import-CSV "D:\Batch2.csv" | foreach {New-MoveRequest -Identity $_.alias -TargetDatabase DB01}"