As reported by one of my players, they get an error message when trying to promote a pawn. They won this game by checkmate another way, but it looks like something conflicts when opening the second GUI for piece promotion while already having the board GUI open

As reported by one of my players, they get an error message when trying to promote a pawn. They won this game by checkmate another way, but it looks like something conflicts when opening the second GUI for piece promotion while already having the board GUI open