remote desktop over vpn

I have established the vpn connection between the windows server 2003 and winxp client.
after estblishing the vpn connection. winxp to windows server remote desktop connection is working. when i am trying to establish the remote desktop connection between windows server and xp client , at the time connecting vpn connection is disconneted. (remote desktop client to server no problem, but server to client problem).
i was enbled concurrent user in windows xp.