Cannot delete a user.

We have 3 users in our user list that cannot be deleted. Using user manager for domains when we try and delete the user we get an error message saying: “The user does not belong to this group.” The user has all necessary group membership. Get the same error message when trying to delete from command prompt using Net command. This is on a Windows NT 4.0 SP6.a network. Let me know if you need any more info.