Are you completely positive that the file is supposed to have video in it. If you downloaded it, it might be corrupt or a fake. Had this happen millions of times. Just noticed that you used plural in your post, so is this happening to all your avis or just one or few. Judging from GSpot info I'm pretty sure that the file is fake, though.
If it does come out to be not corrupt or fake, then I suggest installing
K-Lite Codec Pack 2.40 FULL. It covers most of the codecs that you would need to watch movies. Also I recommend
VLC, which plays most movies without installing additional codecs.