I have an Apple DP 450 G4, yes, archaic but works beautifully. I created a project a while back on iDVD and created a disk image. I also created a more recent project and also saved as a disk image. I burned my most recent project with no problems but on the older project when I try to burn it, just as it tried to write the lead in I got the error "CANNOT WRITE MEDIUM - Incompatible format". These are Sony DVD-Rs and I had no problem prior to this time. I tried this on 2 disks and still got this error. Any ideas? Thanks.