well... in fact i beleive these are unit related problems. I've had lots of problems with 1gb discs... somehow I managed to recalibrate my unit using the service mode. It was a heck to do it, i had previous experience with my mz r70 in this auto adjustment mode, so after a few days i was able to figure it out. It's something that i don't recomend to anyone, since we still don't have service manuals available for the units... After clearing the NV i had my nh700 completely dead for a few days. I've managed to recover it back, restoring some service mode values that i've read in a list made by the user aiox and running successfuly all the auto adjustment modes. After that i had no problems reading and writing 1gb discs. There was one particular disc that was almost full of errors, and with this adjustment i was able to fill it in, and copy the data back, and all the bits were in the right place (md5 hash checked!) So, just a thought... i think that some units aren't properly adjusted, not the discs that are defective.