Windows 10 ?

[Mobhack]

The game uses an old 1990s third-party game engine (so we cannot go in and fix that library). That was designed before multiple monitors ever existed. Also before the windows task bar could be popped-up, so that is why it must not use auto-hide (Windows returns the wrong screen area as far as the old DirectX (5.0?) version the library uses is concerned).

So the game will most likely want both its main window and the windows task bar to be both on the same monitor at start-up (when the library determines the available window area).