iSquint help

I am having trouble converting certain videos in isquint. i ripped a .vob file from a dvd, and when i try to convert it to .mp4, isquint only converts about a minute or so (the video is about 20 mins long). this also happens happens with a .avi file i have, and isquint only converts about half of it, and then says it's finished. i have converted other .avi files successfully, but this one doesn't seem to want to convert fully.

what should i do? should i buy visualhub, or is it a problem with the video itself?