why can't I make a digital recording of a DVD?

Hudsonhawk, you were right- I had it set to dolby digital and when changed it to PCM, was able to make the digital recording. Awesome! Thanks for the tip.

Thanks everyone! I guess I'll try an analog copy first and see how it sounds. Like Rwwear, the purpose of the copy is to listen to it on CD in my car- it's a concert video. What's so frustrating is that the owner's manual of the CDR says that under SCMS copy protection rules, "you can record digital program sources onto a recordable CD disc to create a first generation digital copy. You cannot, however record from this recorded CD disc to another recordable CD disc." If the sound quality is not acceptable, I will look at other options.

Ok, new problem. I got the DVD's that were recorded in dolby digital 5.1 to record to CD by changing the player setting to PCM. I've got a few concert DVD's that were recorded in PCM, not dolby digital, and now they won't record. Any ideas? thanks!