Maybe what I experienced is a related problem.
I created .mp3 files for my website, and QT4 played them flawlessly.
I then uploaded them to my server, then downloaded them via my webpage. Nothing that I can see has changed; file name is the same, "get info" says it's a QuickTime file, etc. After downloading them, QT4 doesn't recognize the files at all. Liquid Player plays them fine. Any ideas?