I created a small test mp4 (compressed) that worked in both WMP and quicktime, and then tried a larger one that did not.
Any ideas?
Dennis
In general I would recommend that you use VLC (http://www.videolan.org/vlc/) as your player for video files. Works on Windows, Mac OS X, *BSD, Linux and so on.
MPEG-4 is a great format so unless you are forced to use WMP then I'd stick to it.
Test both files with VLC. If both files work then it's probably WMP having codec issues.