WinXP and Samba 2.2.2 problem

[Andrew de Quincey]

I've got a weird problem with one installation of windows XP Pro. Something
I have done to it has knackered its SMB system... but I don't know what.

I'm using samba 2.2.2 as a PDC on my network. I have two windows XP client
machines (with roaming profiles)

The machines are able to join the domain fine. (I have checked that the
machine accounts exist fine etc)
(I've tried leaving and rejoining a couple of times as well)

I've disabled "sign and seal", and "require strong passwords" in the local
security policy, but this doesn't help (with THIS problem)

On the first machine, when i attempt to log on to the domain, I am
successful, and my profile is successfully downloaded etc.

On the second machine, however, I am told that I was unable to be logged on
because the PDC could not be contacted (or the machine account doesn't exist
etc)

I have been running a packet sniffer on this network....
On the first (successful machine), I can see traffic on ports 137,138, and
139.
I see some traffic on 139, a NetBIOS name lookup request, followed by more
traffic on 139 as the profile is downloaded.

HOWEVER, on the second machine, I can only see traffic on ports 137, and
138. In fact, all I can see being sent when I try to log on is a NetBIOS
name lookup request for my local domain name (which is successful BTW),
followed by a connection to \MAILSLOT\NET\NETLOGON. After that, there is no
traffic whatsoever (i.e. the CLIENT machine sends nothing else), and the
machine claims the PDC cannot be contacted.

The annoying this is that the second machine was reinstalled recently, and
COULD logon.. but I must have changed some setting which has stopped
everything from working!!!

Does anyone have any ideas? This is really getting annoying!

Oh, nmbd, reports that a successful lookup on my domain name occured, and
then that it is processing a logon request (which according to the logs is
successful)

smbd reports absolutely nothing for the second (unsuccessful machine).

I can obviously reinstall the duff machine, but I'd rather know what it is
that has gone wrong, so that I don't do it again!