You can never take it for granted. Always verify the burned data.
It only takes a couple of minutes.

I agree with easterbunny, the burst rate is too low. Check that DMA
is enabled for the CD/DVD burner and for also for your hard-drive
before and after the burn. Check that you are using the correct
IDE drivers. Which mainboard/chipset are you using? Try
removing the controller card and use the on-board IDE
only.

Next time you burn an image with Nero, save a log and post
it here. Don't forget to remove your serial number from the
log file before you post it.

Try burning the image with the Create Disc tab in CD-DVD Speed.
Use the save button (floppy disc icon) to save the PNG. This should
save a reasonably sized screenshot. The last one was too big for
my little 19in monitor