We need much more info, especialyl wheere those files are coming from, what version of OSX and QT you are using and all that... The first warning is covered here: http://forums.adobe.com/thread/1037126?tstart=0
Um, is iMovie Pro -- aka FCPX -- even recommended for use with Snow Leopard? Don't you need a more up-to-date operating system?
I don't think AE's capable of reading your video files; what kind of media container and codec do those cameras of yours use?
What version of Quicktime do you run?
Do you have any transcoding software like MPEG Streamclip (free), Handbrake or Apple's Compresor? How 'bout QT Pro, even?
The second warning is simply because After Effects does not support that particular kind of file or, in this case, the file is corrupt. If you rendered this video from another program before moving it to after effects, try changing some of the settings related to the kind of file that is made.
Personally, I'd ditch that buggered-up QTX in favor of QT7. X has never worked well.
There's a consensus building here that the problem stems from the footage itself. So again I must ask about the media container and codec of your footage. Unless somebody has the precise same cameras as you, they probably wouldn't know those two items, but you should.