Help with an .avi: Red Color Bars instead of the show

I just downloaded a television program with an .avi extension. Normally I have no problem with this, the program play sfine. But for some reason when this download is finished, all I see are red color bars. I have actually tried three other copies of the same television program and had the same problem. What do I do?
(I am a Mac User, by the way.)
Thanks so much.

I have the same problem, and I am running a PC, so its not a mac issue...