I removed a server that was added into a Remote Desktop Services Manager MMC snap-in. Once the server was removed, the MMC would freeze.
You could notice that the RDS group (in this case ‘My group’ would get an hour glass on it, and then the RDS Manager would get an error.
Close the MMC, and ensure there are not instances of mmc.exe running.
Open the registry and navigate to:
Find the server that was removed and delete it. Close the registry and open RDS Manager.