HoMM3 HD is a mod (add-on) for the game Heroes of Might and Magic 3.

I have an HD mod, and the resolution is set to match my monitor.

Have you considered that if you add scroll bars, a toolbar, and other elements to the game window, which has the same resolution as your monitor, the overall resolution will be larger than the screen resolution? And how do you expect to fit it if it doesn't fit? Naturally, the game will crash.