Dear LIGHTNING UK!
First of all many thanks for your answer.
Yes, I know that is a old drive, bur very reliable, and when I researched the problem here in the forum, I performed cleaning with a disc from Fellowes, but the problem persists.
I've tried also in a Pioneer DVR-216D and the problem repeats itself, so I can not tell if the problem seems a new DVD's shipment of 25 units per box, whereas previously used the 50 units but was now out of stock.
Thanks and kind regards,
quim_pt