Problem joining XP Pro to NT Domain

I have a user in a remote office who has upgraded his computer to Windows XP Professional.

The remote office is has a routed leased line connection to us.

The problem:

When the user is trying to join the computer to our domain it comes up with the error “A domain controller for the domain NAME could not be contacted….”

The name and password he is using when trying to join the domain have been given ‘admin’ and ‘domain admin’ permissions.

He is using the same TCP/IP settings that were previosly working fine on his old box.

He can ping our network.

Any ideas? (Apart from telling him to get a proper OS that isn’t going to breach the network when it eventually decides to work!!).

All comments appreciated.