Hardware or Software - Dual Layer burning problem

The problem - almost every time I try to burn a dual layer DVD the burn fails part way through, ruining the dvd. I've tried many different programs, DVDFab, ImageBurn, DVDCloner, and problem a couple more I've forgotten about. It doesn't happen EVERY time, maybe 1 out of 10 times it works. Is this a burner issue or a software problem? I've got an older (at least 3-4 year old) Samsung 203b burner, I've tried updating it to the newest firmware and I've tried slowing the burn speed to the lowest, still usually makes the nice, expensive dual layer disk into a nice, expensive coaster. Any suggestions?

Dirty laser lens?