Well, and what system? You need to be more specific. "It doesn't work." is not a useful way to ask for help. On a general level, though, it means that you have issues with your system's video Codecs or extensions like Quicktime...
I have After Effects CS4 and my operating system Snow Leopard.
When I mean it doesn't work, I mean it won't load up when after it pulls up that error message. I'll click on the After Effects icon, it'll load as usual, then it'll pull up that error message.
After Effects warning: a compressor used in an output module template could not be found. The animation compressor will be used instead. ( 44 :: 18 )
I click okay, it closes, and then I have an error saying that Adobe After Effects has crashed.
Whar did you change about Quicktime since the summer? Please don't say you opted for that God-Awful QTX. You need version 7.