I have a MacBook Retina.
Whenever I attach a secondary screen, projector or monitor and select the "Mirror Displays" option, the secondary screen turns all black.
It does not matter what connection I use. I've tried the following, and they all have problems:
- MiniDisplay port to a Cinema Display
- HDMI to HDTV
- MiniDisplay -> VGA/DVI converter -> projector
It does not matter what resolution I use.
It all started after connecting it to a projector, where all other presenters using PC was having similar problems.