Thanks! i tested the multiplayer game. when a player turn the page, the other player won't see the page changed, but that player which turned the page will disconnect after select a character.
it's because every running NTT game is independent, if anyone's operation results is different from the others, the connection will be broke.
the solution is that replace all button_pressed_nonsync() in the code with button_pressed(). that means every turning will be synchronized.