samba - Mar 2005 - Problems authentication against ADS on a W2K3 Server

I'm trying to get Samba set up to use ADS authentication against a
Windows 2003 Server running in native mode.  I have successfully joined
the domain, and

	kinit user@MYDOMAIN.DOM

works successfully.  I can also use smbclient to connect to shares on
the local machine, so Samba is basically working.  However, when I try
to connect from a Windows machine I get


	[C:\]net use \\unx02\pub
	The password or user name is invalid for \\unx02\pub.
	Enter the user name for 'unx02': user
	Enter the password for unx02:
	System error 1326 has occurred.

	Logon failure: unknown user name or bad password.

On Unix I get:

	[2005/03/23 17:17:48, 1]
smbd/sesssetup.c:reply_spnego_kerberos(173)
	  Failed to verify incoming ticket!
	[2005/03/23 17:17:48, 1]
smbd/sesssetup.c:reply_spnego_kerberos(250)
	  Username MYDOMAIN.DOM\user is invalid on this system

in 92.168.1.105.log, and 

	[2005/03/23 17:17:48, 0]
nmbd/nmbd_responserecordsdb.c:find_response_record(220)
	  find_response_record: response packet id 34265 received with
no matching record.
	[2005/03/23 17:17:48, 0]
nmbd/nmbd_responserecordsdb.c:find_response_record(220)
	  find_response_record: response packet id 34266 received with
no matching record.

in nmbd.log.

I tried leaving & rejoining the AD domain but that didn't help - in fact
it may have made it worse as prior to that I didn't get the "Failed to
verify incoming ticket!" message, just "Username MYDOMAIN.DOM\user is
invalid on this system".  

If I specify a different username - foo - which doesn't exist in the AD
domain I get 

	[2005/03/23 17:48:21, 1]
smbd/sesssetup.c:reply_spnego_kerberos(173)
	  Failed to verify incoming ticket!
	[2005/03/23 17:48:21, 0]
auth/auth_domain.c:domain_client_validate(199)
	  domain_client_validate: unable to validate password for user
foo in domain MYDOM 
	  to Domain controller \\W2K3DC. Error was
NT_STATUS_NO_SUCH_USER.

in xpclient.log so it is talking to the AD to some extent. 

Interestingly and curiously with I specify an invalid name the record
gets logged in the log file based on the machine name, but where I
specify a valid name it gets logged in the log file for the IP address.
Why?

My smb.conf file is:

	[global]
     	   workgroup = MYDOM 
	        server string = unx02
     	   printcap name = /etc/printcap
	        load printers = yes
     	   cups options = raw
	        log file = /var/log/samba/%m.log
     	   max log size = 50
	        socket options = TCP_NODELAY SO_RCVBUF=8192
SO_SNDBUF=8192
     	   dns proxy = no
	        idmap uid = 20000000-33554431
     	   idmap gid = 20000000-33554431
	        template shell = /bin/false
     	   password server = w2k3dc.mydomain.dom
	        realm = MYDOMAIN.DOM
     	   security = ADS
	        winbind use default domain = no
	[homes]
     	   comment = Home Directories
	        browseable = no
     	   writeable = yes
	[printers]
     	   comment = All Printers
	        path = /var/spool/samba
     	   browseable = no
	        printable = yes
	[pub]
	   path = /var/SAMBA/public
	   public = yes
	   only guest = yes
	   writable = yes
	   printable = no
	   browseable = yes


And my kbr5.conf file is

	[logging]
	 default = FILE:/var/log/krb5libs.log
	 kdc = FILE:/var/log/krb5kdc.log
	 admin_server = FILE:/var/log/kadmind.log

	[libdefaults]
	 default_realm = MYDOMAIN.DOM
	 dns_lookup_realm = false
	 dns_lookup_kdc = false

	[realms]
	 MYDOMAIN.DOM = {
	  kdc = w2k3dc.mydomain.dom
	  admin_server = w2k3dc.mydomain.dom
	  default_domain = mydomain.dom
	 }

	[domain_realm]
	 .mydomain.dom = MYDOMAIN.DOM
	 mydomain.dom = MYDOMAIN.DOM

	[kdc]
	 profile = /var/kerberos/krb5kdc/kdc.conf

	[appdefaults]
	 pam = {
	   debug = false
	   ticket_lifetime = 36000
	   renew_lifetime = 36000
	   forwardable = true
	   krb4_convert = false
	 }

I'm using Samba Version 3.0.10-1.4E on Centos-4, connecting to a Windows
2003 Server AD domain with all the current hotfixes & patches installed,
and I'm testing the connection from an XP Pro machine with SP2 and
subsequent patches.

Any help or pointers would really be appreciated.