I bought a set of two copy-protected DVDs which I was not able to play correctly. They stopped and hopped periodically. I then bought DVDFab Gold and copied one of them to my hard drive. When I tried to play it from the hard drive I got the same behavior.

Sounds like the originals were maybe burned (bluish color) instead of pressed (silver) or else just bad. Most places will exchange discs that won't play.

Thanks for your suggestion; it is probably the right solution. I briefly thought about this simple possibility, but I got hooked on the thought that may be the copy-protection scheme is playing tricks on me, mainly because both DVDs (part I and II) had the same behavior. By the way, they seem pressed and not burnt.

Another user had some discs from Germany that had some new type of protection on them. The program developers always have to play catch-up. Usually new encryption won't be read correctly and will pop up the email notification box in DVDFab. The fact that they won't play even in a standalone player is what leads me to think they are defective, but you're right, what are the odds of getting two defective discs??!? Are these from a major studio?