"Error: A duplicate mailbox was found due to problems during a Move Mailbox procedure. The duplicate mailbox has been deleted. Try again later." - I queued up a lot of mailboxes to move from one store to another in Exchange 2003, and had to cancel the operation before it was finished. The cancel was taking too long, so I killed it. This caused Exchange to fail to clean up some half-moved mailboxes, so when I tried to move them again later, I got this error. The errant mailboxes show up in the target store as disconnected.
As described, the new move procedure finishes the clean-up that should have happened when canceling the previous move. Run cleanup agent on the target store to purge the errant mailboxes after this error, and rerun the move.
This event occurs when you try to move a mailbox because there is latency in the Recipient Update Service, or in Active Directory replication. See ME274119
to solve this problem.
As per Microsoft: "The mailbox could be corrupted. The MSExchUserAccountControl object might not be present on the user object in Active Directory. The user object might not have an X.400 address. The size of the mailbox might be larger than the Exchange store limit that has been set". See MSEX2K3DB
for additional information about this event.