UltraVNC

I tried renaming the DLL then set up the WIN logon again, now I get this message... You selected ms-logon, but the auth.dll was not found. Check you installation.

I have 2 machines both running XP Pro. Have installed Ultr@VNC server on one and viewer on the other. If I don't use the windows login options and only use the VNC password it all works fine. When I try to activate windows login and try to connect I get the following error:
Unhandled exception in ...