Maybe IMAPI problem?
That is the Windoze XP integrated burning program.
Open your system disk (the one Windows is on, e.g. "C:") and click
"Search", for name enter "services.msc". Double-click it, in the right half, find "IMAPI-" or so, doubleclick it, Stop the service, change the Starttype to "disabled" "off" or so (I have German XP, so u need to search a little bit - a picture is at end of this post).
Then retry burning.
Maybe you would like to put a DVD-ROM in the drive before you burn and use Nero Toolkit -> Nero CD-DVD Speed to find out whether you get the required speed
... 2x (2,770 KB/s) instead of 2.4x (3,324 KB/s) ...
Dont think you could write the DVD slower like you can with CD-Rs! IIRC the speed, laser power, sensitivity of the chemicals in the dye only work in narrow constraints. Like buying 8x media and burning at 2x does not ensure you get a better result, and so maybe burning your 8x media with 2x is just too slow, "overheating" or so the dye.
Not sure though ...
Look below This is in German but I guess you will see what I mean -> the IMAPI line is what you have to doubleclick, "Stop", "Disable".