Win2k Terminal Services Licencing

I have a win2k SBS server running terminal services. It’s been running quite happily for a while now. However, it’s now refusing connections and returning the following error:
“The remote computer disconnected the session because of an error in the licensing protocol”.

I’m using WinXP client machines and the remote desktop client to access this server through a VPN.

I’m assuming it’s down to the licences not being installed correctly, but I’m not sure of all the ins and outs of that. Perhaps someone could advise me where to go and what to do?

Thanks 🙂