Our OAB was working fine for the better part of a year after the migration from 2003 to 2010 but the other day it stopped. Here is what I did to fix it. Figured this might help someone else down the road.
- Make sure the System Attendant service is running and is not giving any errors.
- Then open the Exchange Management Console and go to Organization Configuration and click Mailbox.
- Now click the Offline Address Book tab then highlight your offline address book and click update in the action pane.
- Click yes to the question asked and then check your event logs and make sure the OAB was in fact regenerated.
- Now restart the BITS service and then restart the "Microsoft Exchange File Distribution" service.