When a Microsoft Server idle session limit policy rule is configured , users experience an "Idle timer expired" dialog box which is displayed when a session is left idle for the group policy specified amount of time.

Message: 

"Session has been idle over its time limit.
It will be disconnected in 2 minutes.
Press any key now to continue session."

Configure Timeout and Reconnection Settings for Remote Desktop Services Sessions

Note: This courtesy warning message is part of the Microsoft Server Operating System and is not configurable.

Problem Cause

From Microsoft:

"This behavior occurs if a policy setting enforces a time limit for idle Remote Desktop sessions. If an active session has not received user input for the time that is specified in the policy setting, the session disconnects. Pressing a key closes the warning message that you receive two minutes before you are disconnected. However, this action does not reset the idle timer. To reset the idle timer and keep the session active, you must provide user input other than the keystroke that closes the warning message."