Exchange 2010 – Couldn't switch the mailbox into Sync Source mode

If you trying to move mailboxes you may encounter the following error:

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.