Once a server has exceeded 2 connections (in a typical config) you will get the error "terminal server has exceeded max number of allowed connections". I get this all the time after my net drops.

I found a cool way to get around this other than logging on locally / rebooting the system. Remote desktop also has an option for a console login (just like if you were to be at the physical system). This will allow you to have a 3rd session in which you can disconnect your expired sessions.

To do this type
mstsc /v:ServerAddress /f /console

(the /f is for fullscreen and /v is the server/IP you are connecting to)

NOTE: this will only work if there is no one logged in locally to the system I beleive.