Open root folder of your forum, find index.php, edit it with notepad (etc). Find at line 35 'mark' => array('val' => $seo_mark, 'keep' => $keep_mark), after add 'ntheme' => array('val' => request_var('ntheme', ''), 'keep' => true, 'force' => false), 'delete_cookies' => array('val' => request_var('de...