What kind of authentication you are using for TS Users? Active Directory or on the box authentication. In both cases, I would try to create a dummy user with same permissions level as your issue user and see if that works.Assuming that this person is not a Master, I would make him a master and see if it works for you.HTH
We have on the box authentication for TS users. And there are few other users with same permissions level and the workflow just goes fine without any error for them. We even tried asking the user to logon from a different machine, assuming the problem might be with the user's machine, but same results using both IE and FF. I have raised the ticket with Interwoven as well. Need to verify adding the user to local administrators group and try.