Some co-workers and myself were having the same problem. This worked for us:
Delete the service book tied to the account you're having problems with on your BB (Options -> Advanced -> Service Books then find it and delete it.)
Next, login to your BIS and delete the account you're having trouble with. Then, re-add it from scratch.
This should work. If you notice two mailboxes on your BB after this, just pull the battery, count to ten, put it back in and you should be back to normal.
Original thread: OWA Integration Failure
Let me know if it works...