Escape Puzzle - Vampire's Castle

This is probably the last of the escape puzzles that I would recommend. The puzzle itself was fine but the escape part of it was ridiculous. Sort-of Spoiler below. There was one "challenge" that borderline made me angry but the rest was great and hard! SPOILER... Sort of There is a part where you have to work with roman numerals and they make sense as they are seen. But the mirror is a clue telling you to read them backwards. This works fine for one of the numbers but the other makes NO SENSE. Even Roman Numeral websites say the number isn't valid. There is one website that Ravensburger links to in their clues and that sites explanation of that number is so garbage.