Make sure that file ./modules/mod_ajaxrecommend/mod_ajaxrecommend.php has sufficient rights (at least CHMOD 644, or if that doesn't work, try 755). If directory modules/mod_ajaxrecommend/ is CHMOD 777 change it to 755.
Try to access the file directly through your browser (http://www.domain.com/modules/mod_ajaxrecommend/mod_ajaxrecommend.php). You should get a text response and not Error 500 nor Error 403.