I'm not sure what I've done recently that might have totally screwed up Quicktime Player but it won't play anything (MP4, MOV, AIF, nothing!). However, I can preview videos in Finder and iTunes can play any of these files no problem. WTH? Has anyone ever seen anything like this? I've tried uninstalling flip4mac and Perian. I've tried reinstalling OSX ML using the recovery partition. Nothing seems to fix it. This is the error I get... not very helpful.