The latest news on the series of QuickTime 7.4 blunders is that this version is incompatible with Adobe After Effects, a Mac OS X software. It basically prevents After Effects from rendering video content. Apple’s response to this is to delete posts on their forum describing the problem. Anyway, the only way to solve this is to use the Time Machine to roll back your system to a pre-7.4 state. If you have not installed QuickTime 7.4, don’t do it.
This is the latest in the series of QuickTime 7.4 debacles. I have previously mentioned about how QuickTime sets file and MIME settings to the QuickTime player even when asked not to, as well as about the stupid QuickTime installer.