I dont know how I can help with one user.
Maybe you can issue queries against the database if you know the proper information for him.
Like example if his old userid is 12 and the new one is 23 those queries would do it
UPDATE pp_photos SET userid=23 WHERE userid=12;
UPDATE pp_comments SET userid=23 WHERE userid=12;
The problem here is if you ran the userfix script which should query your vb
database based on the guys name to get his userid I would be more concerned why his userid is not found meaning is this guy really in vb
Thats more likely your issue. Remember we cant directly support changing integrations because of all the mess. I can provide tools and tips which we have but its not foolproof here.
I would really suspect that this guy does not exist in vb
therefore there is nothing you can do other than have him register in vb
then do the userfix script or rather you register him.