Hi, it's a bit confusing because you wrote down X-plane 11 in the title.
Anyway, have you tried to run the installer again, to see if any file needs to be corrected?
A second option would be to try and delete (or move for backup) your X-plane 10\Output _Preferences folder. You will loose all your joystick and keyboards settings though.
There is no reason why it should stop working, because X-plane 10.51r2 has been the last version for almost a year now...