I have the exact same problem and have been dealing with it for almost a year. I can’t open ProRes files in QT X but I can in QT 7, I can’t space bar preview ProRes files but I can preview .mp4 and h.264 files. This cause’s FCP and Premiere Pro to lock up when loading project files. Also compressor locks up too.
I have re-installed FCP twice and I have tried to re-install QT X with Pacifist. I have tried to re-install QT 7 from the install disc. I even copied QT codec components from another computer and replaced them but no luck.
Has anyone had luck figuring this out?