Try updating the B_PosterId in all of his/her posts.
1. Determine his/her U_Number
2. Run a query like this:
update w3t_Posts set B_PosterId = <his/her U_Number>
where U_Username = <his/her Username>
Hopefully that would do the trick, although with the join in the query, you shouldn't see any posts if the B_PosterId doesn't match.
Give it a try! (And backup your database beforehand!)
-Lance
