Authentication failure on some users- Ev

NT 4.0 SP6a – IIS – Front Page
Some users are failing authentication when trying to access secure web pages. They are using the correct user name/password but their systems are passing the wrong domain and they are not being request to supply the domain.

I am using both basic authentication and challenge response to accomodate both IE and Netscape users in (IIS).

I have set up user group/user with log on locally rights in User Manager for domains.

NTFS file security read permissions are set to allow both the group/user.

Front Page – Security permissions allow browse access as well.

What am I doing wrong?