Sorry I have been so slow to respond. It now seems pretty clear the problem is with the LG GH22NS50 reading. I have read elsewhere that Nero's verification in some circumstances is suspect yielding false positives, so beware if it is valuable data. Today I used the Lite-on DH16AYH for both burning and verifying, it worked perfectly with ImgBurn. I plan to give DeepBurner a try. If it points to ImgBurn I'll report.
Thanks, John.