Had the same problem. My (temporary) solution: in wp-content/plugins/all-in-one-event-calendar/app/controller/class-ai1ec-events-controller.php on line 120 remove or comment
wp_enqueue_script( ‘jquery.tools-form’, ‘https://cdn.jquerytools.org/1.2.5/form/jquery.tools.min.js’, array( ‘jquery’ ), ‘1.2.5’ );
Hope this helps for you too!
Robert Busschots
