Currently Being ModeratedJan 12, 2013 10:57 PM (in response to RJN13)
To follow up - I opened the iPhoto library I imported into Aperture using iPhoto and the same video thumbnails that are scrambled in Aperture display fine / video playback is fine is iPhoto (v9.4.2).
Currently Being ModeratedJan 13, 2013 12:13 AM (in response to RJN13)
I suggest to check the video codecs you have installled; if you use Perian or have a flip-camera, you may have an incompatible video codec installed, see: http://support.apple.com/kb/TS4155
Why was a TimeMachine restore necessary? And did you use any helper/uninstaller/cleaner utilities, before you made the backup or after restoring? Sometimes this kind of helpers remove too much. I this case you may need to reinstall Mt. Lion to restore missing system components, that are not included in your TimeMachine backup.
Have a look at this thread Re: Import video to Aperture library on Mountain Lion,
and also at the post: Re: Import video to Aperture library on Mountain Lion in the same thread.
To reinstall from the "Recovery partition" see Linc Davis's post here: Re: Garageband doesn't open in Mac Mini mid 2011
Currently Being ModeratedJan 13, 2013 10:06 AM (in response to léonie)
Thanks leonieDF, the support threads you referenced led me to the solution.
For some reason the com.apple.xpchelper.cache file was missing in my /System/Library/Caches folder. Thankfully someone had posted the file to dropbox and shared on the thread. Adding the file to my folder and rebooting solved the problem.
Others reported re-installing Mountain Lion from the recovery partition fixed the issue as well, likely re-installing this file in the process. It makes me uncomfortable to find my Time Machine recovery didn't fully recover the OS so I'm going to re-install Mountain Lion just to be safe.
For reference, here is the dropbox link to the missing file: