Glad it worked! I've run into that once or twice...
All I know is one library is older than the other - checking that box enables the older library. This is all open source stuff, so I suspect the developer of the older project simply stopped working on it at some point; then someone came along and started working on their own solution.
I've run into it quite a few times... I would't be able to say how many times it's happened to me with DVDs I've ripped, but it's at least a dozen. The strangest thing was that with some DVDs, it would even occur with individual titles whilst others on the same disc would work perfectly! Like I said, I'd been banging my head against a wall for over a year with it, unable to find a remedy on Google, so thanks once again for posting the solution!
libdvdread is a subset of libdvdnav. HB originally only used libdvdread ... however we added libdvdnav as it helped with going through an actual dvd's navigation code to try to get to the main chapter ... now that said ... sometimes libdvdread was left in so in cases like this it could be used to try to bypass ... among other things the famous "99 titles" type of content protection. Now that said its not foolproof. But therein lies the diff.
Personally, fwiw, I leave it on libdvdnav (default) which more often than not gets it right. Ultimately on tough sources I go with open source title specific, which doesn't let libdvdnav follow a bunch of erroneous bogus titles.
Thank you for the explanation! So the 'libdvd' options are purely for navigating the DVD's titles?
I wasn't aware that you could directly open a specific title, that's one to bear in mind! Using the tip posted here (using libdvdread) I've successfully been able to encode all of the DVD rips that had been giving me issues. Following your advice, I've re-ticked libdvdnav, and will leave it ticked until such a time as I run into any more problems.
Thank you again for all of the help posted in this thread!