Thanks for the reply. I updated the firmware, that didn't affect anything. My DVDs are mainly Intenso by the way. Are they the same as Ricoh?
I came to the conclusion, that my DVDs are corrupted. It has been 10 years, since I burned them. Some DVD5 are also bad.
I tried Recuva (doesn't support DL for some reason) to recover some of them. The problem is, that the movie is playable up to a certain point. So that doesn't help much.
Are there better programs that do a better job or should I forget those DVDs that cannot be read or copied?