Only burns to 99%, this started out of the blue..

Hi, the problem I am having is the following: no matter what software I use, all of a sudden I cant burn DVD's no more. When using Nero the program stops at 99% and restarts, the disc is lost. Like I said I have used other software, to no avail either. This is getting hopeless, I have lost quite a few discs already. I tried updating the firmware I downloaded from NEC website, (2.1) but that tells me: target is not found correctly. And stops there...
As far as I can see there is no good explanation on what to do next on the NEC website.
Windows tells me that the drive is working fine, has the latests driver etc etc. This drive reads fine, btw. The problem is with the burning, that all of a sudden and out of the blue didn't work anymore...
All help is appreciated!