Maybe you'll find some answers here:
I had a similar issue with ProRes 4444 files - editing on FCP, came back to a project after two weeks and when I tried to match back to a clip, all I saw was white - heard audio, but no picture. Sure enough the source files wouldn't open either. I did a reformat and reinstall of 10.6 and now they play down without a problem.
The general consensus in the forums is that Security Update 2011-006 or iTunes 10.5 is causing this error in random Quicktimes. Hope this helps.
I found a work around.
You need to be able to access a machine that has not been updated with the latest quicktime update. (I installed Snow leopard on a spare drive so I could use this process) In the updated system folder/library delete the components and quicktime folders. Empty the trash. Then in the non-updated System/Library copy the components folder and the quicktime folder and paste them into the updated system/library folder. (make sure you have already deleted and emptied the trash of the offending folders or this won't work). Restart the computer. It should see all files as it did before. Worked fine for me.
Hope this helps