There is a bug with Windows 2000 Terminal Server. Sometimes certain clients, when remotely connecting will pick up a Temporary license which will last 90 days. After that time you wont be able to connect.

You can delete the temporary license on the client side to allow you to re-connect.

Use the registry hack to remove the keys....

(Note: use right click and save as, then run the file from your pc) 

FixTempLicenseWin2kTermServ.reg