Followup on DVD-R Media

[Rob Lewis]

While trying to back up my hard drive to Apple-brand DVD-R media, 
Retrospect tried three times with fresh disks  and every time aborted 
after a while with "Trouble writing media. Error 206 (drive reported a 
failure: dirty heads, bad media, etc.)"

Interestingly, after each failure I had to reboot the machine to get 
Retrospect to even see a new disk in the drive--otherwise it would 
report "there is no disk in the drive."

I have no problem backing up to CD-Rs (other than the fact that they're 
1/6 the capacity and 1/3 the speed of DVD).

Anyone have any insight? System is a dual-800 QuickSilver G4 with 
built-in Superdrive. OS X Server 10.2.3.