Yeah, I know, they’re still running WSS 2.0 at my employer. I’m just here to help, not judge. = )

So I get the request (and I got it before and forgot how I did it) from
a site admin that they can’t add a user to their new website they created. It
says they already exist when clearly they do not in the Manage Users screen.
This is generally because the SID of the existing user account doesn’t match the
SID of the new account you’re trying to add. The solution? Well documented in this Microsoft KB article.

The quick solution? If it’s a WSS site that is hosted on the portal
site, go here:

http://ServerName/Sites/SiteName/_layouts/1033/Siteusrs.aspx

Otherwise go here:

http://ServerName/_layouts/1033/Siteusrs.aspx

Obviously replacing “servername” with your server and “sitename” with the parent site
you’re trying to add the user to. Locate the user in the list, check the box and
at the top click the “Remove Selected Users” link. Once gone you can now safely
add this person to the parent and/or child sites without issue.