Currently Being ModeratedOct 13, 2012 8:49 AM (in response to markusruebe)
you may accidentally have started your Mac in Save Boot Mode. Then the advanced features of your Graphic Card are disabled and Aperture cannot run, see: Mac OS X: What is Safe Boot, Safe Mode?
This can happen, when you turn on a wireless Mouse or keyboard while booting.
Try rebooting. Does it solve the problem?
Currently Being ModeratedOct 13, 2012 11:22 AM (in response to léonie)
thanks for your reply - well I was NOT in Save Boot Mode.
I also had no BT Mouse or KB connected.
I rebooted the System, deleted .plist - right now I uninstalled Aperture to do a re-install - I will see, how it works.
If not, I will go to the Genius Bar ...