Most likely a GPU/video driver glitch.
Have you made sure you have the latest version of ACR?
Don't think so. I have the latest 7.1 ACR version and the GPU/Video works just fine for everything else. Once I convert the RAW file and start working in PS6 it all looks fine there too. If it helps, I can do a screen grab of the wierd ACR panel and post it here. Like I said, everything was working fine post 10.8 installation untill about a week ago.
Even when I go to PS6 preferences and select Camera Raw this black background control panel for ACR shows up. I downloaded the 7.2 Release but can't seem to find where to select it to see if that works. I seem to remember being able to select different versions of ACR from the ACR control panel but that must be obscured by the descibed glitch too.
How can I completely uninstall and reinstall ACR? Seems like the updates are patches now.
Thanks for any help
So FWIW, I solved my problem by re-installing the MAC OS 10.8.1 operating system. Have no idea why this happened but I'm glad its working again. Thanks for trying to help.