Well, if you rotate 180° its ok again, so it's either a 90° error or where the King/Queen are standing on the wrong board colour, sides of each other (e.g. Quee

Well, if you rotate 180° its ok again, so it's either a 90° error or where the King/Queen are standing on the wrong board colour, sides of each other (e.g. Queen on right), or not facing their opposite piece (K facing K). I'm fairly certain when I was a kid that I made all those mistakes when setting up the board.