Thanks for the reply.
I have burnt about 30 of them and when I check the IMGburn logs about 50% show the "Program Memory Area Update Failure" message. But the data seems okay, some of them are RAR volumes and they extract okay....my understanding is that Winrar will give an error message if any of the data is corrupt.
Also I extracted one and did a sfv checksum, and then went back and compared the checksum to the original and it was a match. So hopefully the data is okay.
Anyway I will be able to try a different burner next week so i'll see if that fares any better.
Thanks again for the info, I won't buy from this seller any more if the discs are not the good ones.