Could be a poor quality film, but probably a codec problem. Try using a different player.
VLC media player has the codecs built in and is very reliable. I keep it on hand just for files that won't play right in WMP. It's a good back up for other players.
For WMP,
K-Litecode Codec Pack gets recommended a lot. I use
XP Codec Pack 2.0.6 and rarely have any trouble playing a file.
More info:
http://www.gnutellaforums.com/tips-t...p3-fixers.html