"Supported Disc Not Available"

I just burned a disc for a client in DVD Studio 4. I used a quicktime source file that I've used a bunch of times before. I drag it into DVDS4, set it as 'first play', and burn the disc.

After the disc burns, my Mac Pro tower won't even find the disc. I get nothing - not even a grayed out file on the desktop. The DVD plays fin in a PC laptop, and in two over-the-counter DVD players.

Why won't my Mac Pro even recognize the disc? Is there a setting somewhere that I tripped over?