A couple of things to check.
First check to see if it happens everywhere, or only from their PC. If it is only from their PC, go to their browser and delete all history and cookies. The cookie that Enterprise looks for to start with might be bugged. (I learned this one trying to fix my NT login problems)
If it happens everywhere...
Check with the user first to make certain that they don't have a large number of items in their personal directory. (I have found users get a little touchy when you delete those).
From the CMC. Delete the user then go to Authorization and update the NT domain import.
Because of the error message, it sounds like the problem might be that their user folder is corrupt. Deleting and reimporting the user should hopefully fix that.
Lisa