Fro Joomla 2.5.x Paste the code on line in helper.php file below
defined('_JEXEC') or die('Restricted access');
defined('_JEXEC') or die; if( !class_exists("ContentModelArticles") ){ require_once JPATH_SITE.DS.'components'.DS.'com_content'.DS.'models'.DS."articles.php"; }
For Joomla 3.x – Paste the code below
defined('_JEXEC') or die('Restricted access');
if(!defined('DS')) define('DS', DIRECTORY_SEPARATOR); if( !class_exists("ContentModelArticles") ){ require_once JPATH_SITE.DS.'components'.DS.'com_content'.DS.'models'.DS."articles.php"; } if(!class_exists('ContentHelperRoute')) require_once (JPATH_SITE . '/components/com_content/helpers/route.php');