Burning disks

Hi. I have 3 Macs: an iMac 3 years old, a Powerbook 3 years old, and a new MacBook Pro. I have the same problem with all three of them regardless of which system update I have (it's currently 10.4.7). Trying to burn disks - any CDs or DVDs, any brand, fresh from container, I get the same message: Sense key = illegal request Sense Code = 0x30, 0x05 CANNOT WRITE MEDIUM - IMCOMPATIBLE FORMAT. I've used Toast, Mac the Ripper (in the old days), iDVD and Disk Utility. The Apple burner typically allows me to prepare the disk, and nearly completes burning when it quits. It also warns "The drive reported an error: Sense Key - MEDIUM ERROR Sense Cody = 0x0C Write Error.
My hard drive has plenty of room, I'm at a loss. And why are these warnings so cryptic?!