Try getting Verbatim DVD+R DL 2.4x MKM-001-00 Made in Singapore blanks, since they seem to have better support than the Verbatim 8x MKM-003-00 ones.
I see you're using Dee's 1.O4 firmware on that burner, and according to the overview of writing strategies, that firmware doesn't use the latest strategies available for DVD+R DL. If you can, try the Liggy's AD-7170A Bitsetting Firmware 1.04.