samba - Jul 2004 - Windows 2003 Terminal Server - domain users not being able to log on

I have set up Samba 2.0.4 on Fedora Core 1 as the PDC for the domain, 
and we have a Win2003 server as a member server w/ Citrix MetaFrame 
Presentation Server 3.0 installed. Domain users can log in locally just 
fine, but only local users can log in through Citrix or RDP. When a 
domain user tries to log on remotely, Win2003 rolls the progress bar for 
a few seconds, and then responds:

The system cannot log you on due to the following error:
The specified domain either does not exist or could not be contacted.
Please try again or consult your system administrator.

Does anyone have any clue what's going on? Samba logs reveal nothing I 
could understand -- no identifiable error messages.