Site-Wide Security Deletion Problem

[kgreer]

I am trying to delete some users from the site-wide Security. The server is no longer on the same domain as the users I am trying to delete. The error it gives me is below:

The user or group name 'abb\kgreer' is not recognized. (rsUnknownUserName)

Is there another way of deleting the accounts instead of using the Site-wide Security?