[Samba] samba server as domain member

[medusaXX at uni.de]

i have got a windowns 2000 server with active directory. i added a computer 
record for my samba server and tried to add it to the domain:
smbpasswd -j medusaxx -r beta -U admin

but i got this error:
Delta:/etc/samba# smbpasswd -j medusaxx -r beta -U admin
Password:
Unable to join domain MEDUSAXX.

here is my smb.conf:
[global]
	netbios name = DELTA
	server string = %h server (Samba %v)
	security = DOMAIN
	encrypt passwords = Yes
	obey pam restrictions = Yes
	password server = beta
	passwd program = /usr/bin/passwd %u
	passwd chat = *Enter\snew\sUNIX\spassword:* %n\n 
*Retype\snew\sUNIX\spassword:* %n\n .
	restrict anonymous = Yes
	syslog = 0
	max log size = 1000
	socket options = IPTOS_LOWDELAY TCP_NODELAY SO_SNDBUF=4096 
SO_RCVBUF=4096
	dns proxy = No
	wins server = 192.168.0.1
	guest account = 
	invalid users = root



anybody can help me ?

yours sincerely 
medusaXX