I finally got a disk to burn.
I uninstalled Nero 9 and then reinstalled.
Tried to burn project using +DL disk- went to layer break
and then got error.
I re-coverted the Xvid file again using avi2dvd, this time using single
layer format instead of dual layer.
Burned again using different media (4.7GB -R). Success.
At this point I don't know whether it was the media or the conversion
(avi2dvd), but at least I know the burners work. Going to buy a different
brand media (DL) and see if I can get it to work also.