I had a support call this morning, the guys were unable to connect to a remote 2003 server via 'Remote Desktop' anymore ever though it worked the night before. The message was something like "You can to be a member of the Remote Desktop users group to access this machine remotely".

We had no choice to to cab over to the data center and look at this on the console. Terminal Services were running and the users in questions were still part of the Administrators group which also gives them remote desktop access.

The clue was in the event log. A warning was stating somethine like 'No licensing server found'. I asked the guy how long ago this machine was set up and it was only a few months ago.

Microsoft changed the terminal server set up with Windows 2003 server, the previous 'Administrator mode' a maximum of two users who have to be administrators at the same time, is now enabled by default even without installing 'Terminal Services' in the Windows components setup. However if you install them there you get the old 'user mode' which requires a 'Terminal Server Licensing' service and licenses which costs money. The tricky thing it that you can use 'user mode' for 2 or 3 months without the service but then it seems to stop working completely. This had happened last night.

So uninstall 'Terminal Services', reboot and enable 'Remote Desktop' via the System properties dialog. Works fine again.

In Windows 2000 you had to set up the service even for admin access, that's why people still do it in 2003.