Problem with NEC 3500AG DL Burning

OK. Can anyone help ? I have NEC RW ND-3500AG Dual Layer Burner, firmware version 2.16. It will not burn Dual Layer Discs. as soon as the burn starts, it ejects the disc, telling me it is a non compatible disc, it has perfoprmed an illegal operation. I have tried 3 different brands of Blank disc, but still no luck. HELP !!!

Update the firmware to NECs latest (2.1b) & only ever use Verbatim +R DL media.

Thanx. Works perfectly !!!