samba - Apr 2003 - Windows XP - Samba Domain join problems (Wrong Parameter)

Hy everybody out there!
 
I?ve got a problem when I try to join my Samba Domain with a Windows XP Pro.
Client. When I try to join the domain and entered the Admins username, there
comes the error window Popup "Wring Parameter".
 
The strange thing ist that I have already a client in the Domain... :(
 
Maybe I did something wrong with the second one? 
 
I hope anybody of you can help me!
 
Thanks in advance!
 
Andreas Kauffmann
 
Germany