Hi Boomer,
Alpesh's recommendation is a good sanity check. If this proves not to be the case, I'd probably take a look at the AES logs to see what's going on during the client login:
c:\AdminStudioEnterprise\wwwroot\Logs\####.log
This should show you some communication with the domain controller, and perhaps some specific query results. I would post excerpts during the attempted user login--you should be able to see the username in the log when this is taking place.
Post some excerpts if you can.
--Cary