As far as I know the English DVD versions of the game do not require a CD key to be typed in. Depending on the error message, it could just be from the copy protection system used (Securom, at least in the English releases).
Try using a different optical drive, if available; I've seen the lowest drive letter one recommended, with comments that Securom can be picky if there are multiple optical drives.
I believe Securom
also has a utility to remove / update / reinstall their drivers.
You could also try contacting the publisher, at the email address listed in the manual (possibly firstname.lastname@example.org).