If you trying to move mailboxes you may encounter the following error:
![Exchange 2010 - couldn't switch the mailbox into sync source mode Exchange 2010 - couldn't switch the mailbox into sync source mode](https://wwwedwardvbs.files.wordpress.com/2015/01/move-request-error.png?w=300)
Solution:
Change the TCP KeepAliveTime for the servers involved in the move. Source, Target, and CAS.
KB: http://technet.microsoft.com/en-us/library/dd349797(v=WS.10).aspx
Hope it helps.