No domain server available

I am haveing a problem with one system running XP Pro loggin onto our Domain. We have three servers at our head location, Win2000 and 2 Win 2003 servers. At the location where this user is we have a Win NT 4.0 Server. our locations are connected together via a Firewall with a VPN. This user has logged onto our network before with out problems. Now all of the sudden they get an error “No domain server available” when they try to log on. I can connect to their PC remotely and they can ping all the 2000/2003 boxes. We did recently make some changes , they were remove 3 NT 4.0 Servers includeing our PDC and replacing them with the 2 2003 Servers. Note the xp PC was connecting to both and then today can not.

Any ideas ?