Happy ripping!
If you are seeing this message, don't panic. You haven't broken your drive, and your disc isn't necessarily faulty. You have simply run into the ongoing "arms race" between encryption protocols and ripping software. makemkv volume key is unknown
There is nothing more frustrating than slotting in a brand new 4K Blu-ray, firing up MakeMKV, and waiting for that sweet sound of your disc drive spinning up... only to be met with a wall of red text and the dreaded error: "The volume key is unknown for this disc - can't decrypt." Happy ripping