Apple appears to have stopped including several important codecs, including Photo JPEG and the PNG codec (which is needed for pre-keyed footage) in the latest versions of Quicktime 10. If you are having trouble using our footage, you may need to download good ol' Quicktime 7 and install that as well. Then reboot, so your editing software will have access to all the codecs.
If you are on windows, go here:
and if you are on OSX go here:
Download and install the software, and reboot. Should get things working!