jos-Error: Unable to load renderer class

JSite -> render() @ /var/www/oftangou_www/htdocs/index.php:48
JDocumentFeed -> render() @ /var/www/oftangou_www/htdocs/includes/application.php:271
JDocument -> loadRenderer() @ /var/www/oftangou_www/htdocs/libraries/joomla/document/feed/feed.php:201
JError :: raiseError() @ /var/www/oftangou_www/htdocs/libraries/joomla/document/document.php:926
JError :: raise() @ /var/www/oftangou_www/htdocs/libraries/joomla/error/error.php:251