ressurecting this because there's absolutely no information about this problem on the net. I've been searching for two days and have found the exact same thing: one person asking the question, and a bunch of uninformed people responding.
My setup is a dual boot leopard and win7 desktop and a powerbook g4 1.5 ppc i'm working on for a customer.
Tiger burns fine on a dvd-r and boots and installs.
The powerbook won't recognize blank dual layer dvd's and spits them out.
The matsushitu uj-825 drive doesn't support burning of dual layer discs, but it is indeed capable of reading them. Yes EVEN +R burnt dual layer discs, as i've known several people to back up leopard and run it on even OLDER revisions of the superdrive.
The problem does indeed lie within the bitsetting but that's not all. The utility posted above doesn't work for every mac either. But saving the image as a decompressed .cdr and burning it in windows with imgburn set to bitset as a dvd-rom WILL allow any of these drives to access the disk MORE EASILY. My powerbook even mounts the disc 1 out of 5 tries with this method.
The problem is that over the years the laser goes in these drives. Typically the first thing to go is the capability to read +dl and +r disks. -R are second to last to go and -rom is the last. This isn't always so systematical, but it is typical. Opening up the drive and bumping up the dvd voltage by lowering the resistance on the potentiometer for the dvd laser will allow it to more easliy read +r and +dl disk for a few months to a year before it dies a horrible death.
Best bet. Install from target disc mode on another mac, or order a newer superdrive off ebay. (or pop the hard drive out and use an adapter to put in a mac desktop.) i went through 5 discs before i realized it was simply failing hardware that was the problem.