Remote Desktop Problem

I have a client who remotes into his work computer using rdp through a vpn. I just set him up a new computer and it seems after a while rdp stops working and i’m not sure what is causing this. When rdp stops working you can still ping the machine and the machine still gets online. After it stops working when you click on connect in the rdp client nothing happens. No errors no nothing. The only way to get it to work again is rebooting the machine in the office. I’ve tested this on 3 remote machines and they all do the same thing when trying to connect to the office machine.

The remote computer is running winxp pro sp2.

Any idea or thoughts on this?

Thanks