If you have been using Remote Desktop Successfully on Windows Server 2012 for around 120 days and are suddenly unable to connect, you may need to reset the Remote Desktop 'timebomb' registry key.
NOTE: Using the regedit program is dangerous and we recommend against using it unless you are aware of the problems this can cause, this should only be used by advanced users. Please contact our support if you are uncomfortable with the steps provided here:
Goal: Use the regedit program to Delete the Windows Server 2012 Remote Desktop timebomb registry key
Steps: Open the regedit program->Browse to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Terminal Server\RCM\ and expand
Right click on 'GracePeriod' ->Permissions ->Advanced-> Change Owner: Network Service to Owner:Administrator, check the option to apply to all subcontainers, Apply->Apply->now you should be able to delete the L$RTMTIMEBOMB key which is the REG_BINARY type
Then reboot and you should now be able to connect via remote desktop again, however this issue may repeat itself 120 days from now.