No audio from an XVID .avi file

Question

I have never had any other playback issues with this player, but I think this may be the first XVID .avi file I have tried. Other divx .avi files work properly. I have searched for a firmware upgrade to no avail. Any tips would be greatly appreciated ... including where to find a freeware program to convert xvid audio to standard divx audio without reencoding the video stream.