New NEC ND 3550A DVD Burner

I just bought and installed a new NEC 3550A burner. For the most part, it works very well. I have a few DVD disc that were burnt about 50%, when I tried to burn these for backup, it burnt OK, but when it burnt past 50%, it continued to read and did not say “burn successfully” as usual. I have to turn off computer to get it stop.

I am new to burning DVD disc, so any advices would be greatly appreciated.
What should I do now?
Thanks

Upgrade your dvd burning software (Nero perhaps?)

I 've used Nero Ultra Edition 6.6 and it works well… As I stated, this only happens when I burn 50-90% fully burnt disc… Other than that, it always say " burn successfully". Any other advices? Thanks