The problem is that your mapped key is doing exactly what you told it to. It is sending CTRL+ALT+1 to the game (i.e. a target of Slot1). ISBoxer does not send keystroke commands back to itself, so you cant get it to send CTRL+ALT+1 and expect it to execute it's own hotkey to swap windows.

What you really need there is a Window Focus Action, not a Keystroke Action.