I’ve had similar problems in the past (but not recently). Anyway, this question come up every so often and I don’t remember ever seeing a definitive answer. The general suggestion is to try different/better/name brand media, and/or try a different type (DVD +R, instead of -R, etc). I suggest posting your problem again in the DVD Studio Pro forum on the Cow, maybe you’ll get a better answer. Sometimes, just burning another disk will work, so you may want to try a couple more. Try your disk on different Mac’s as well – if you can.
https://forums.creativecow.net/cgi-bin/new_view_posts.cgi?forumid=155
Tony!