I have a question I am working with WSS version 2 and can not add a
user to a specific site collection. The user had access and the owner
of the site accidently removed him and when we attempt to re add him we
get this message.

Can not add the user because a user with that name already exists.

This user does not show up in the UI as having access to the site so I
ran stsadm.exe –o enumusers for this site collection and the user still
does not show up. I even tried STSadm.exe –o delete user command which
says it completes successfully but does not actually fix the issue. Any
idea's on what could fix this or even if you could point me in the
right direction I would greatly appreciate it.