User can't login after posting a new thread.

[Fungsten]

What happened is a user posted a thread and right submitting it VB logged him out. Now he can't log back in. I checked the thread and there were two duplicates and came up with a server error something like the thread can't be found on this server.

Now, the user has deleted out the cookie and rebooted. Has changed browsers and switched machines. I was able to logon to the account and there were no problems. Just for the heck of it I went to the ACP, cleared out the Cache file, Repaired/Optimized table and fixed the unique indexes. The user STILL can not login.

TIA.