[Samba] NT Backup can't connect to samba 3.04 share

["Olaf Eichhorn, Vermessungsbüro Pfeifer"]

I have upgraded samba from 3.0.2 to 3.0.4 on our Fedrora core 1 server. 
(server role = standalone)
All programs (e.g OpenOffice.org)on the Winclients work perfect with the 
servershares. They can read, write...
Only the NT-backup program from 2000 and XP can't connect to the mapped 
networkdrive. But it worked under samba 3.0.2. I know the NT-backuptool 
isn't very good, but it worked for our needs.

Where can I start to troubleshoot??

Olaf