Get Nero InfoTool and find out what Region Control and Region Code is. For best result, you want None for Region Code. Check out Digi/Mango's region free page, download the utility, free your drive and try again.
What ripper are you using? DVD Decrypter? Try something else like cladDVD XP and see if it works. If that doesn't work, get DVD Region Killer from Elby and set Auto Region. You'll need to have CloneCD installed before Region Killer.