K, this is how i fixed it.
Go to database, find the user, and delete everything from
- vbp_oldgroups
- vbp_history
The user can now log back inagain, cos his/her histroy has been wiped.. how to prevent this from occuring again? well, i suggest ensuring your pplaza is set up right, i.e. everythign you want in it set up. Then, once thats been done run an update on the db (backing up first) clearing the above collumns.
Now there will be no chance that anyone has history for items that no longer exist.
my pennies worth.