Hi, I am not sure if this is a hardware or software issue.
I recently purchased a Pioneer DVR-109, it is a great drive DVD-R wise, burning 8x discs at 12x. With CD-Rs it seems rather picky. Burn-at-once and Alcohol 120% report Plextor and Datawrite discs at 4-speed only, and Creation discs at 32, 24, 16, 10, or 4-speeds. Any ideas on what I can do short of buying different media?