He's trying to copy Underworld Evolution---a recent movie. This may have a newer protection scheme that Decrypter can't handle on its own, or may in fact have dirt or a scratch that is interfering in the decryption process. I don't own this movie, so I can't say if it has extra protection on the disk or not.
Inspect the disk for scratches and/or dirt. If this doesn't seem to be the problem, download RipIt4Me and use it. The RipIt4Me site has plenty of instructions on how to use the program, so do some reading there.
Or you could try DVDFab Decrypter, or AnyDVD.