If its a copy of an original then there is probely not a copy protec. on it ,its mostly a bad copy ,get a new one , other wise use dvdcrypter and check the option over rule read error in I/O options , it somthimes helps .
My suggestion to all of you who have prob. whit reading discs buy a Lite on reader and use Dvd Rebuilder or DVD Fab Paltinum if none of the other pices of software dosen't seems to work out !!!