Welcome to the Forum.
Unaware of exactly what â€œNexxtech DVD-R 16X mediaâ€ actually is.
Suggest providing the Media MID (Manufacture ID and Media Code) (Example: TYG02) of your â€œNexxtech DVD-R 16X mediaâ€. To obtain the Media MID (Manufacture ID and Media Code) (Example; TYG02) of your â€œNexxtech DVD-R 16X mediaâ€ use a software utility similar to DVDInfo (http://www.dvdinfopro.com).
In seeing that your â€œNexxtech DVD-R 16X mediaâ€ is off the wall unknown quality Media it is not unusual for you to experience difficulties with this particular Media.
Suggest obtaining known proven quality error free Media such as Taiyo Yuden or Verbatim Media which has an excellent track history of consistently producing quality error free results.
I can assure you that â€œNexxtech DVD-R 16X mediaâ€ is not on any NEC-ND-2500A DVD Media Compatible list but the known proven Taiyo Yuden or Verbatim Media is.
For NEC-ND-2500A Firmware suggest visiting Liggyâ€™s & Deeâ€™s NEC Firmware Web Page. Perhaps one of Liggyâ€™s & Deeâ€™s NEC-ND-2500A Firmwares with provide better results with your â€œNexxtech DVD-R 16X mediaâ€ ->