sounds like the TOTALLY wrong forum for this to me....
based on your description it sounds like the problem occurs somewhere during the transfer from your computer to youtube. Try exporting the movie in a different format (if possible,) or converting it with some other utility to a different format before uploading it.
I mean, if the video looks fine in YOUR computer... then the problem has to do with youtube. Contact them and/or ambrosia (snapz developers)
Also, to cover your bases, you should try emailing a copy of the video to somebody (someone running windows for a compatibility check) and see if they can view it. If they can, then youtube is the problem.