samba - Feb 2003 - Domain member server starts logging "change_trust_account_password: Failed to change password for domain" after one week

Hi,

I am running a Samba printserver (2.2.7a).
I have successfully joined the domain with
smbpasswd -j NTROBOTIC -r robpdc2 -UAdmin%
Eactly one week after joining the domain , the samba server starts 
logging: (prining still works)

[2003/02/27 13:05:04, 2] lib/util_sock.c:open_socket_out(874)
  error connecting to 129.247.189.234:445 (Verbindungsaufbau abgelehnt)
[2003/02/27 13:05:04, 0] rpc_client/cli_netlogon.c:cli_net_req_chal(246)
  cli_net_req_chal: Error NT_STATUS_INVALID_COMPUTER_NAME
[2003/02/27 13:05:04, 0] rpc_client/cli_login.c:cli_nt_setup_creds(47)
  cli_nt_setup_creds: request challenge failed
[2003/02/27 13:05:04, 0] rpc_client/cli_trust.c:modify_trust_password(142)
  modify_trust_password: unable to setup the PDC credentials to machine 
129.247.189.234. Error was : NT_STATUS_UNSUCCESSFUL.
[2003/02/27 13:05:04, 0] 
rpc_client/cli_trust.c:change_trust_account_password(248)
  2003/02/27 13:05:04 : change_trust_account_password: Failed to change 
password for domain NTROBOTIC.

What is the problem?
Do i have to take care of a case sensitive wirting of the DOMAIN name?
A part of smb.conf follows...

Thank you very much

Greetings

Hansj?rg

 [global]

log file = /var/log/samba/log.%m
log level =3
security = domain
workgroup = NTROBOTIC
encrypt passwords = yes
password server =  129.247.189.234

netbios name = PRINTSERVER
server string = PRINTSERVER
announce as = NT Server
wins support = no
wins server = 129.247.189.234

preferred master = no
domain master = no
local master = yes


-- 
_________________________________________________________________

Dr.  Hansjoerg Maurer           | LAN- & System-Manager
                                |
Deutsches Zentrum               | DLR Oberpfaffenhofen
  f. Luft- und Raumfahrt e.V.   |
Institut f. Robotik             |
Postfach 1116                   | Muenchner Strasse 20
82230 Wessling                  | 82234 Wessling
Germany                         |
                                |
Tel: 08153/28-2431              | E-mail: Hansjoerg.Maurer@dlr.de
Fax: 08153/28-1134              | WWW: http://www.robotic.dlr.de/
__________________________________________________________________