Issue in the AJAX action

I get the following error when using the ajax action wpex_titles:

PHP Warning: Invalid argument supplied for foreach() in /website/wp-content/plugins/wp-experiments-free/wpex.class.php on line 247

In the following piece of code, the casting of $_POST[‘id’] as int in the foreach causes the issue:

    public function ajax_titles()
    {
        $titles = array();
        $images = array();
        if (isset($_POST['id']))
        {
            $cur_page = isset($_POST['cur_id']) ? intval($_POST['cur_id']) : null;
            foreach ((int)$_POST['id'] as $id) {                                           // <====== this line is causing the issue
                $images[$id] = array(
                    "old" => get_post_thumbnail_id($id)
                );
                $titles[$id] = $this->titles("", $id, true, $id == $cur_page);
                // the titles() call will update a global variable which will
                // effect the return result of get_post_thumbnail_id
                $images[$id]["new"] = wp_get_attachment_url(get_post_thumbnail_id($id));
            }
            echo json_encode(array(
                'images' => $images,
                'titles' => $titles
            ));
            die();
        }
    }

If you could fix it that would be awesome!