If you're iMRCHNT RDP session is frozen you can use the keyboard shortcut  

At the same time hit keys CONTROL + ALT + END (if your keyboard doesn't have a noticeable END key, try CNTRL + ALT + FN + Right Arrow)

This will bring up a blue screen with the following options

Click on Task Manager

1. Select IM_MainMenu

2. Click on the End Task Button

You should then be brought back into the iM login window.

If for some reason that doesn't work. Do Control + Alt + End again and select SIGN OUT

Other RDP Keyboard shortcuts you can use are:

Try pressing Alt Insert.

Then you can loop through the open programs so you can logoff or start another session.  

Or to help you move through open windows or take screen shots: