Requiring Catagories

You can do this by adding following code in your theme functions.php

add_filter( "adverts_form_load", "my_adverts_form_require_category" );
function my_adverts_form_require_category( $form ) {
    if($form["name"] != "advert") {
        return $form;
    }

    foreach($form["field"] as $k => $field) {
        if($field["name"] == "advert_category") {
            $field["is_required"] = true;
            if( ! isset($field["validator"]) || !is_array($field["validator"])) {
                $field["validator"] = array();
            }
            $field["validator"][] = array( "name" => "is_required" );

            $form["field"][$k] = $field;
            break;
        }
    }

    return $form;
}

Is there a reason this function no longer works?

Nevermind, I see you added the option to the widget.