Make sure that the Exchange Monitor application is closed before you uninstall. Because the application stays in the System Tray you may think that the app is closed but it is still running. I would suggest checking the system tray and to be 100% certain make sure that the app is not running in the Task Manager.
Hope that helps.
That did it, Sham, thank you. It wasn't open in my session, but one of our techs left a remote desktop session open... closed it and it uinstalled flawlessly.