error 100 "device rejected command" with eMac CD-R

[MacDr]

I'm so frustrated by error 100 during Normal backups, causing "Execution incomplete" during the "Comparing" stage. The Log reports: "Trouble reading: 1-Backup Set A (566), error 100 (device rejected command)."

 

It's always able to complete "Copying" stage successfully; but then five minutes into "Comparing" the error 100 appears. Has occurred dozens of times, although at other times I can complete an entire 900 MB backup without error.

 

*** NOT a 10.4.7 upgrade issue: I've been seeing this error for months. ***

 

Tried numerous brands of disc (Sony, Maxell, TDK, HP, Verbatim). I can still always do "Finder burns" (manual copy of items in Tiger to blank optical disc) to Verbatim CD-R without error. Took eMac to Apple Store for diagnosis and they found nothing wrong with optical drive. eMac otherwise working perfectly.

 

Tried deleting all scripts, backup sets, all eight preference files in Library/Preferences/Retrospect (including even my Retro.config file), and then starting over from scratch: re-entered license key; ran new "Custom Configuration tests" on this drive and media (Successful each time); but same issue quickly reappeared.

 

I understand from reading other posts that "two brands are commonly recommended for use with Retrospect, these are TDK and Verbatim. It is also recommended that you use +R/RW rather than -R/RW. In most cases +R/RW will afford better performance." I am using Verbatim; and my eMac's drive supports only -R/RW.

 

What else can I do to stop error 100? Thanks.

 

System specifics:

Retrospect Backup version 6.1.126

Retrospect Driver Update, version 6.1.6.100

 

Apple eMac 1.42 GHz PowerPC G4, purchased 9/2005

Built-in, original, tray-loading ATAPI DVD-ROM/CD-R/CD-RW (HL-DT-ST RW/DVD GCC-4481B), Firmware Rev 2.05

Mac OS X 10.4.7 (but this issue has been happening for months, with 10.4.5 and 10.4.6 as well)