This usually occurs if you have a corrupted database and only part of the user information exists.

It is most often caused by someone messing with the database using phpMyAdmin, but it can also happen if your db has been trashed for other reaons (as could occur before Elgg 1.5 for example.)

The problem is present in the table elggusers_entity if 
you have the backup just restore it, if no 
installation and start a new query to get the new bank 
created and is replaced by that of only problema.Depois with the insert in the table with data from former users 
I hope I have helped