samba - Jul 2005 - samba PDC and access to unauthorised shares from w2k client

I posted this problem before, but still didnt get any solution.
I have a Samba 3.0.14 server as PDC and several w2k clients.
I got a problem when a user tries to access an unauthorised share on the Samba
server.
Instead of the usual message box 'Access Denied' the user gets a message
box 'Enter network password' on his pc.
When trying to access an unauthorised share on one of the other clients, from
the same client and with the same user-id i tried to reach the share on the
Samba server, i get the usual msj box 'Access Denied'.

I dont know what this problem is. Both as well the user and machine have a valid
account on the PDC.

This problem i never had before with Samba 2.2 and i really have no idea where
its coming from.
If a user wanna access an unauthorised share the 'Access Denied' has to
show up in stead of the box asking for name and password, right?
Even if i fill in an user-id which has access rights to this share in the format
DOMAINNAME\USERNAME and PASSWORD i get a msj box
'The credentials supplied conflict with an existing set of credentials'
Can someone help me with this problem pls. Im really stucked and dont know where
to look anymore.
If needed i can send log-files, packetdumps and/he smb.conf.

Joshua