Are you logged into one of the sites? wp_ajax_nopriv_ hooks will not fire if the user is logged in, so if you’ve only used that hook, the AJAX request will not work at all if you are logged in.
You will need to hook both wp_ajax_nopriv_mp_throwcontent_2 and wp_ajax_mp_throwcontent_2 for it to work with both logged in and logged out users.