Accept please that I'm not disputing your description of your writer. But are you "sure" your unit only accepts +Media? I'm asking because my unit from Dell a 3450A indicates in the Properties that it is a +R/RW only. But I've burned many -R disks. Look at your order from Dell and see if it doesn't say "DVD +-/R/RW."
This is only a suggestion because I really don't know squat about DVD burners!