have you installed the AC3 filter yet it is something that has been brought up a few 1000 times here, and also stated at the bottom of most of the hosts pages.http://ac3filter.net/
I think the newest Divx update has finally got this built in ??? I don't use Divx or even have it installed so I couldn't tell you for sure without reading some searches.
VLC on the other hand has all needed codecs built in. That is why it works with almost everything and my choice of player.
So try installing http://ac3filter.net/
for your system type and see if it fixes it