This generally happens when you try to use Shrink on a movie with structural protection.
You might try DVDFab on this movie. It is an all-in-one program for decryption and reducing the size of the movie. The free trial will be fully functional, and when the trial period ends, the decryption/ripping section will still be functional. At that point you'll need to rip with Fab, then compress with Shrink. This is the best combination if you want a free solution to backing up dvds.
The only caveat is that the free section (DVDFab HD Decrypter) will lag behind the paid version on encryption capabilities by 30-60 days.