Alright, you have an NEC 6500a dvd burner, which is certainly new enough to handle either +R or -R disks. You didn’t show the manufacturer ID on the blank disk, but we’ll assume it isn’t very good media and go from there.
Since your burner works fine for RW disks, it sounds like there is no problem in the software or the DMA status of your drive.
Does Nero recognize the fact that you have loaded a blank disk into the drive? Or does it simply say to insert a blank disk?
If it does see them, can you burn anything, or is it simply screwing up the burn somehow? Have you tried burning at 8x rather than something faster?
One possible step to take is to get known good media (blank disks). I recommend Verbatim 16x blank dvds, and try to burn them at either 8x or 12x rather than full speed.
Edit: Thanks for the additional info. Some people have had poor luck with MBI disks, but it isn’t universal. I still think going to Verbatim might help.