I have subtitle films that I received on dvd. I am working in FCP

I got the films into fcp by exporting them to quicktime, 100% quality, dvcpro 50 Pal- (the movies are pal)

The QT files have frames missing here and there, so there's a stutter in the video. Happens every minute or so. Any idea what this might be? The original dvds don't stutter.