[support] Drupal CAS Configuration

Has anyone had much experience with the Drupal CAS module? I'm attempting to use it for an SSO implementation by integrating it into a site that I am developing where there is a central CAS server that will manage the users for all other sites we have. This Central CAS server will have access to a central repository of user login informaiton.

The issue that I'm seeing is that there are a few specific users that I have that will be maintained by Drupal and when I attempt to Login as those users, it does not seem to authenticate me. Is this possible to have it set up this way? Am I barking up the wrong tree?