lightbox bug

why does lightbox works only in some sections ?

the code i have trouble with 

        if (elgg_is_active_plugin('reportedcontent')) {
            elgg_unregister_menu_item('footer', 'report_this');
            elgg_register_menu_item('extras', array(
                'name' => 'report_this',
                'href' => 'reportedcontent/add',
                'text' => elgg_view_icon('report-this') . elgg_echo('reportedcontent:this'),
                'title' => elgg_echo('reportedcontent:this:tooltip'),
                'link_class' => 'elgg-lightbox',
                'priority' => 500,
            ));
        }