If enough remote desktop users end their sessions by just closing the window instead of clicking Log Off you can run into the following error:

The terminal server has exceeded the maximum number of allowed connections

Here is how you can resolve the situation by ending the hanging connections.

Type the following in a dos prompt:

mstsc /v:<ip to remote machine> /admin

Once logged in, go to Start -> All Programs -> Administrative Tools -> Terminal Services Manager

Now on click on the name of the remote machine in the left panel and the logged in users will be shown in the right panel.

Right-click on each one and click Reset.