Was he running in cached mode? You say you deleted his oab, if he was running in cached mode delete the .ost as well. When he re-starts his outlook it will re-create the .ost. If the problem persists, check the event logs on the exchange server where his mailbox resides and you should see an OAB error there. Please post the exact errors from the event logs. That will help us help you find the problem. Thanks.