Every time I've run into this issue - it's been due to database import issue, or a problem with mis-configured GUEST.ADMIN passwords.
However - I do know that Nick ran into an issue similar to this around CU04. You may want to take a look at the following post and see if it helps:
http://www.otmfaq.com/forums/f26/new...-836/#post2060 ([NEWS] OTM v5.5 CU04 has been released)
--Chris