Moving Exchange Mailboxes between Sites

I am trying to move individual mail boxes between 2 Exchange sites within the same Organizational Container. I have followed the steps from the TechRepublic article “Moving individual mailboxes between Exchange sites”. The move fails with the following error:
“Failure,”Cannot open the Exchange Messaging store (error 141 Copier.cpp:181, MAPI error MAPI_E_FAILONEPROVIDER [0x8004011d]: You do not have permission to log on.)”
I have given the permissions required to the account that is moving the mail boxes.
Any sugestions or ideas would be greatly appreciated.