When ripping from DVD to ipod in DVDFab Platinum 3.1.2.6 I notice that several movies lose video or both audio and video right towards the end of the film, the screen just goes blank, what is causing this problem?

I am ripping into mp4 format and I am increasing the video bitrate each time to improve quality.

Movies I noticed this on are:

Man Of The Year
Catch & Release
Alpha Dog
The Color Purple
etc.