A regular Windows Server 2003 comes with two remote access sessions. This means you can open a maximum of two simultaneous Remote Desktop Sessions at one time, unless you install more terminal services licenses.
However one thing you may not know is, there are actually three sessions! The third one is the actual console session which is displayed in monitor out. You can access that session by launching a RDP session with the server name followed by /admin.
Below is a screen shot of what I’m talking about.
Next time you want to boot a session out you can login to the box via this method and launch tsadmin to logoff the stale sessions.
Speaking of tsadmin, you can also use tsadmin to connect to the remote server and logoff the user that way as well.