It should give that error if it actually can't put your video card into 640x480x256, which I seem to recall WAS something I encountered years ago - some video cards are just too fancy for such a thing. Can't imagine why that would impede windowed mode though. The good news is that you shouldn't have that problem with Supreme WIth Cheese if you want to play that. The bad news is I'm not sure how to fix it for Kid Mystic beyond the things you have tried. Someone else might have an idea? For the most helpful people, check out our discord (link on my website on the About page), where the real knowledgeable people sit.