I've seen this problem and fixed it. Yours might be different but you can try this anyway. Sometimes when you install (or reinstall) iTunes it will skip the install of Quicktime for no reason. This could be the files you are missing. Try downloading and installing the standalone version (the one that does not include iTunes) of Quicktime here: http://www.apple.com/quicktime/download/

If this doesn't work, come back and type out the whole error message you get. Good luck.