CAN'T READ Verbatim Dvd-r 8.5gb 4 Speed Advazo Dual Layer 5pk

Just cut together a video on FCP - and using DVD studio pro I'm ready to burn it. It's 5.1GB and so had to make it a dual layer film. I've just bought Verbatim Dvd-r 8.5gb 4 Speed Advazo Dual Layer 5pk to burn BUT it wont read it. Is this a superdrive issue or have I bought the wrong blank dvd's?

I've got a Powerbook G4 15" Aluminum with:

MATSHITA DVD-R UJ-816:

Firmware Revision: DXJ3
Interconnect: ATAPI
Burn Support: Yes (Apple Shipped/Supported)
Cache: 2048 KB
Reads DVD: Yes
CD-Write: -R, -RW
DVD-Write: -R, -RW
Burn Underrun Protection CD: Yes
Burn Underrun Protection DVD: Yes
Write Strategies: CD-TAO, CD-SAO, DVD-DAO
Media: No