First possibility:
take a look at the disk and make sure it not dirty/smudged, if so clean it. If it's somewhat/badly scratched, shrink could be having a problem with that. If this is the case, you can try using these two free applications which are more forgiving when it comes to scratched disks:
1)Using DVDdecrypter to rip in file mode (rip the whole movie)
Second:
This could also be caused be either Sony's or Microvision's new copy protection on the disk. DVDshrink and DVDdecrypter are no longer updated and can't crack the encryption alone, they need some help, that's where anydvd comes in. Anydvd is a program that when installed runs in the backround to help DVDdecrypter or DVDshrink crack the encryption and get your backup, just use shrink or decrypter as you normally would and let anydvd do the rest. Anydvd is well supported and constantly updated, it comes with a 21 day free trial before you have to buy it.
If you want to try a free alternative, try dvd43, it's like anydvd but has no support and is not as frequently updated. You can't have both dvd43 and anydvd running at the sme time, they conflict with one another.