At certain parts in the film (always the same bit) the video stops and audio keeps playing?
The at low bitrates the DivX codec may drop frames to save space. The playback codec sometimes gets confused thinking that the video has ended or something strange like that. Lowering the smoothness setting on the DivX codec and using a higher bitrate can help to stop this happening usually 75% is enough. If you set the Fast Motion codec to a minimum of 1500-2000kbps this will happen much less. And never use the Low Motion codec under about 600kbps. The only other thing you can try is opening the bit that goes wrong using VirtualDub, re-encode the bad clip and then re-join it back to the original. Check out my joining AVI guide for details on doing this. Other than that I do not know.