PDC refuses some passwords

[Michael Oswell]

I have run into a problem recently which is driving me crazy. :)  

Our current setup is as follows:

FreeBSD 2.2.8 server running Samba 2.0.5a
The Samba server auths against an NT 4.0 Server (SP5).

Certain NT machines in our network (NT 4.0 Server SP4), have problems
accessing shares on the samba server.  After a clean boot, they will be
able to successfully access the shares for about 1/2 hour, at which time
the server begins logging the following:

password server PDC-VAN rejected the password

If I try any other valid username/password for our network on one of these
'bad' clients, they fail as well.  Rebooting the client appears to fix the
problem for about a 1/2 hour, at which time they must reboot again.

Any suggestions would be greatly appreciated :)

Thanks..

Our Conf:

-----------------
[global]
        workgroup               = XCERT
        netbios name            = mac-40
        server string           = Xcert Internal Fileserver
        local master            = no
        security                = server
        password server         = pdc-van bdc-van yared-nt
        name resolve order      = hosts bcast lmhosts wins
        load printers           = no
        printing                = bsd
        dns proxy               = yes
        encrypt passwords       = yes
        debug level             = 3
        socket options          = TCP_NODELAY SO_SNDBUF=8192 SO_RCVBUF=8192
        max log size            = 1024
        lock directory          = /data/samba/var/locks
        log file                = /data/samba/var/log.%m
        max log size            = 4000
        username map            = /data/samba/lib/username.map
        printcap name           = /etc/printcap
        lpq command             = /usr/bin/lpq -P%p
        lprm command            = /usr/bin/lprm -P%p %j
        queuepause command      = /usr/sbin/lpc stop %p
        queueresume command     = /usr/sbin/lpc start %p
        browsable               = yes   
        guest ok                = no
        guest account           = nobody

 -----
Michael Oswell
Xcert International Inc.