Thank you for responding. That potential cause had not occurred to me.
The ripping was all done by DVDFab, which I always have set to remove any copy protection, which is why I'd have thought that copy protection should not be an issue now. I'm also surprised that JRiver cannot play files that other well known programs can. Is there any particular reason for that?
I also have a feeling that the rips did play in JRiver originally, but it is too long ago to be sure, and I may be kidding myself.
I just loaded a sample problem folder into DVDFab, and got the following data:
Disc media: Folder (DVD-Video)
Disc region: 1, 2, 3, 4, 5, 6, 7, 8
Video standard: PAL
CSS (Content Scramble System) protection not found.
RC (Region Code) protection not found.
RCE (Region Code Enhancement) protection not found.
APS (Analog Protection System) protection not found.
UOPs (User Operation Prohibitions) protection not found.
Invalid PTTs, PGCIs, PGCs, TMAPs, CELLs, VOBUs protection not found.
Fake vts protection not found.
Bad sector protection not found.
Structure protection (ARccOS, RipGuard, etc.) not found.
PathPlayer is enabled!
Unplayable cell not found.
full disc copy/play is supported
So that all looks pretty clean.
Has anybody else had this problem, and are there any other potential explanations?