I had recently purchased a 50 disc pack of this brand (National) and my experience with this brand has been nothing other than a pain in the neck.
Before I begin explaining whatever I have done so far, I'll include details about these discs and its manufacturer:
OptiArc AD-7240S capabilities on these discs
Unique Disc Identifier : [DVD+R-DL:MBIPG101-R10-065]
Disc & Book Type : [DVD+R DL] - [DVD+R DL]
Manufacturer Name : [Moser Baer India Ltd.]
Manufacturer ID : [MBIPG101]
Media Type ID : [R10]
Product Revision : 
Blank Disc Capacity : [4,173,824 Sectors = 8.55 GB (7.96 GiB)]
Recording Speeds : [2.4x , 3.3x-8x]
Hex dump of 'media code' block
I have attempted to burn these discs using multiple burners, three, to be exact. None of the burner(s) were able to complete even a single successful burn. Out of the 50 pack, I have already accumulated 15 coasters, with 100% fail rate.
The burners that I used were:
* TSSTCorp SE-208AB
* Sony OptiArc AD-7240S
* Matshita DVD-RAM UJ8E2 (OEM-laptop)
All the burners were of course, updated to the latest firmwares available via the respective manufacturers.
I always used imgburn to burn these discs and at the maximum possible optimized settings after doing proper research. The available write speeds were variable from burner to burner, as the TSST burner offered 3x,4x, the OptiArc offered 4x,6x,8x, while the Matshita offered only 2.4x,6x. I have tried all possible combinations and all possible write speeds in each burner to no avail.
I also attempted to investigate the write strategies present within my OptiArc burner since I believe this is the most powerful and better burner than the other two I have. Initially, on older firmware that the OptiArc came with, there was NO write strategy present for the discs I was using (MID: MBIPG101-R10-065), so I updated the firmware for the OptiArc to the latest available for it (v1.04).
After updating the firmware for the OptiArc, I was now able to find a write strategy for these discs, however, the burn processes still failed. The errors were ALWAYS the same, irrespective of which burner was used, i.e., write error/medium error.
Therefore, I would seriously advice AGAINST purchasing any dual layer discs from this brand name (National), no matter what.
Setting fire to your money would probably be more exciting and enjoyable than purchasing these crappy discs and have to deal with it.