I thought about that Lynne, but the users profile was not broke, it was that the userid was not fully assigned to the user somehow. So by looking for the user in the ACP, he would not show up. Clicking on the users name in List New Registrations would lead you to a profile page in the ACP, but no fields filled out.
Did you take a look at the database? When a user is registered, the userid gets put in several different tables. You can still view some things like the profile, or the user in the admincp if only a couple of tables are filled out. But, you will have other things broken if not ALL of those tables have the information in them. It just would have been worth trying.