No expert, but I've found BCDC and BCFC to be much more reliable on the DW-1650 than BCHC, and they contain a decent write strategy for MKM-001. BenQ USA pulled BCHC from their site, but it should be okay for DL burns. Might even want to flash it with BCDC or BCFC again.
Off the top of my head: Drive stuck in PIO mode? Another program established exclusive access to the drive? Media contains data from a failed or quickly interrupted burn? Failing IDE cable? Might just want to reboot your machine and try again.
