Extraction of CC's only works for a few minutes of video.

I just got some older DVDs with CC. They only contain vob files as the video stereams. VLC will properly decode and display the CCs all the way through the videos, but CCextractor will only decode them to srt for the first few minutes of video, and suddenly stop. Most are 30 minute or less videos. There is no message: it just stops extracting and the srt is incomplete. Is there any reason for this?