Kruser. Found this tip. Don't know if it will help.
"Hi Mike I just read your article about Retrospect 5.1 and DVD Ram drives. (comments from a reader twice in last week's news pages)
Out of interest I decided to test Retrospect 5.0.238 with a DVD Ram back up, and I managed to make it work.
The problem appears to be that Retrospect 5.0.238 can not erase and rename the DVD RAM discs. This error message appears "Couldn't erase disk, error 102 (trouble communicating)."
To get around this problem simply erase the new disk with "Disk Utility" and then name it in the Retrospect convention ie: For Backup Set A = Disc Names are 1-Backup Set A, 2-Backup Set A, 3-Backup Set A etc.
Hope this helps someone.
Cheers, Andy "
http://www.xlr8yourmac.com/archives/jul03/072503.html