Remove any disc from the burner, close the tray, apply the latest firmware available (US09) then reboot your computer. Also try burning at other speeds. As a last resort, you might want to use a cleaning disc on that burner. Have you tried DVD+Rs?
As for those ~10 burnt discs, if you had Verify enabled when your burnt them, and they passed the verify process, then they're fine and you don't need to worry about them.