I've not got a dual layer burner, but I have found DVD Decrytper to be a bit flakey for burning discs. Especially if i have any other software running at the same time (and we're not talking intensive stuff), chances are DVD Decrypter will turn that disc into a coaster. Nero on the other hand has proven constantly reliable.

Its a costly experiment, but trying different software sounds like a good idea before ruling out that batch of DL discs entirely. And if you've not tried it, burning at the lowest speed might be a bit more reliable.
Just annoying that it'll cost a fiver to find out...