Windows XP can't connect to Samba server via VPN

I have a Windows XP desktop(Windows Firewall is disabled) that is attempting to access a Samba share on a Red Hat Linux server. This works every time while on our network. We use the SERVER security setting in smb.conf and our network uses Active Directory to authenticate.

I have another desktop which I attempt to acess the Samba share on the same Red Hat Linux server. This fails every time. I try this using \\IPADDRESS\sharename in My Computer but it fails with the Network Not Accessible message. I try using the Map Network Drive and then use the same \\IPADDRESS\sharename and Connect Using A Different User Name and enter the AD account details. This fails as well with the same message.

While still connected via VPN, I try to access the Windows 2003 server in the same rack (same LAN), it works, with the same AD account details.

Here are the global settings in smb.conf


[global]
        workgroup = DMZ
        netbios name = THESERVER
        encrypt passwords = yes
        security = server
        password server = XXX.XX.XX.XX
        passwd program = /bin/passwd
        username map = /etc/samba/users.txt
        local master = No
        wins server = XXX.XX.XX.XX
        server string = THESERVER
        invalid users = root
        null passwords = no
        ntlm auth = no
        client ntlmv2 auth = yes
        client lanman auth = no
        lanman auth = no
        domain master = no
        time server = Yes
        socket options = SO_KEEPALIVE IPTOS_LOWDELAY TCP_NODELAY
        load printers = No
        printcap name = CUPS
        log file = /var/log/samba.log