-[_NSObserverList setCursorPosition:]
This kind of NSInvalidArgumentException, especially because it's on a private class, is probably due to a Zombie object. You are sending a message "setCursorPosition:" to an object that no longer exist, but another one is in it's place. In this case "_NSObserverList".
Try running with the "Zombie Objects" diagnostics objects to trace down which is the object that should receive that message but was gone. That option keeps the objects in memory when they are released, but marked as zombies.