I tried to capture a 20 year old VHS tape, recorded from broadcast TV (a local news documentary, and a piece of ABC's 20-20 or something) and I got "cannot capture, content is protected." Did they embed macrovision in the signal? Not a commercial movie tape, remember. A later cable premium movie channel recording on the same tape did not produce any complaints. This happened with TWO different pieces of hardware AND at least 2 different software capturers. I then tried it on a different PC, and it didn't complain. So this might be the problem: the PC that didn't like it was Windows VISTA and the one that did was XP. Hmmm. Next I want to try some other tapes, then maybe Windows 7. I don't want to have to buy a macrovision scrubber just yet.
chances are it's inbuilt fista drm picking up a slightly floaty line/field lock from the tape and interpreting it as macrovision. That's how at least one of the macrovision systems worked back when.. the tv would display it fine because of a thing called flywheel line synchronisation.. but the discriminator circuits in vcr's would garbage an attempted recording usually by wrong phase or timing of the colour burst caused by the bad timing variation of the line pulse from the macrovision tape.
That makes sense, because I used an older VCR with Vista and a newer one on XP. I'll switch them and see what happens. And I will check if if the problem segments were EP, obviously wouldn't help for a stable signal.