This problem is affecting both MAC AND PC users. DO NOT UPGRADE. Don't ruin your MP4 encoded movies. Wait until they find a fix.

I've tested all of my movies (unprotected MP4 files) and they do not play on my Mac. Further testing indicates they also doesn't play with QuickTime directly by finding the file in the iTunes folder using QT Player. This is NOT an iTunes problem as I've seen some people say on other boards but definitely a QT problem.

The same "broken" movies do play from VLC so it's a problem with the QT plug-in and/or codec file(s). The "broken" movies also won't play in FireFox via the QT plug-in, reporting a QT logo with the flashing "?" error.

I removed DiVX component and that did not correct the problem. All symptoms remained the same. I tried this because DiVX is famously bad for breaking things. Further, the old standby of deleting preferences files has not changed thing.

Running QT player or Running iTunes and then opening the movie requires a force quit. Running it from within a browser doesn't lock it up, though, just the error.

Movies NOT in the iTunes directory were not all affected and some play