[Samba] Unable to join Win client to domain (user not found error)

[Eric Evans]

Hello,

I'm having some difficulty trying to join a WinXP client to our Samba
domain.  When I try to join the client to the domain and I submit the
computer name and the domain name in the computer identification control
panel, I'm prompted for the root user and password on the server, so I enter
root and the root password on our Samba server.  I then get a message saying
that it couldn't be joined to the domain because the username (i.e. root) is
not found.  But the root username and root account are definitely in the
server password system and in the Samba password file.  Furthermore, the
samba log indicates that the authentication of root was successful:

[2007/08/28 15:12:09, 2] smbd/sesssetup.c:setup_new_vc_session(1200)
  setup_new_vc_session: New VC == 0, if NT4.x compatible we would close all
old resources.
[2007/08/28 15:12:09, 2] smbd/sesssetup.c:setup_new_vc_session(1200)
  setup_new_vc_session: New VC == 0, if NT4.x compatible we would close all
old resources.
[2007/08/28 15:12:09, 2] auth/auth.c:check_ntlm_password(309)
  check_ntlm_password:  authentication for user [root] -> [root] -> [root]
succeeded
[2007/08/28 15:12:11, 2] smbd/sesssetup.c:setup_new_vc_session(1200)
  setup_new_vc_session: New VC == 0, if NT4.x compatible we would close all
old resources.
[2007/08/28 15:12:11, 2] smbd/sesssetup.c:setup_new_vc_session(1200)
  setup_new_vc_session: New VC == 0, if NT4.x compatible we would close all
old resources.
[2007/08/28 15:12:11, 2] auth/auth.c:check_ntlm_password(309)
  check_ntlm_password:  authentication for user [root] -> [root] -> [root]
succeeded
[2007/08/28 15:12:12, 2] rpc_server/srv_samr_nt.c:_samr_lookup_domain(2916)
  Returning domain sid for domain PLAB ->
S-1-5-21-442260237-273426051-107281484

And I have the machine record setup correctly for this client.  I have
joined other WinXP clients to this same domain without any trouble in the
past, but since I upgraded from Samba 3.0.22 to 3.0.25c now I seem to be
unable to join a client to this domain.  So I was hoping someone out there
might have some suggestions for further troubleshooting of this problem.
The global section of my smb.conf is as follows:

[global]
        socket options = TCP_NODELAY
        invalid users = bin daemon adm sync shutdown halt mail news uucp
        print command = /bin/lp -d%p %s; sleep 5; rm -f %s
        printer = 128_1
        printing = SYSV

        netbios name = pleiades
        workgroup = PLAB
        passdb backend = smbpasswd
        os level = 65
        preferred master = yes
        domain master = yes
        local master = yes
        security = user
        domain logons = yes
        logon drive = h:
        logon path =
        logon script = %U.bat

        log file = /var/log/samba.log
        log level = 2
        max log size = 500
        debug timestamp = yes

        encrypt passwords = yes

Thanks!
EJ