but you are not the only one to meet it from what I have read - although that is not quite certain either
I reported precisely the same problem in October last year: http://www.pclinuxos.com/forum/index.php/topic,110147.0.html
One day I just noticed that I couldn't watch commercial DVD videos any more, not even DVDs that had worked a month or two earlier. But I could access the files on data DVDs in the same drive.
I still haven't found a solution. I even cannibalized an older computer and moved its DVD drive to the one with the problem. The problem remained.
The cannibalized drive was an IDE drive, the normal drive was a SATA one.
I just decided I'd have buy a new drive when I got some spare cash. But the strange thing isn't that the drive suddenly stopped working; it's that it stopped working with videos while it continued working with data disks.
After finding this thread I will
set the region code to 2, even if I've never had to do that before with the same drive, and even if most video players in Linux are supposed to ignore the region code.
The cannibalized drive is indeed a Samsung. The one that came with the computer? I'll report when I find my screwdriver. (PCC identifies it as an HL-DT-ST DVDRAM GH40F.)