[Boothby]

Those who have < PHP5.4 can add the following at the beginning of the error_generic plug-in and test it. This is a non standardized method, so it may or may not work.

PHP Code:

if (!function_exists('http_response_code'))
{
    function http_response_code($newcode = NULL)
    {
        static $code = 200;
        if($newcode !== NULL)
        {
            header('X-PHP-Response-Code: '.$newcode, true, $newcode);
            if(!headers_sent())
                $code = $newcode;
        }       
        return $code;
    }
} 


source: http://www.liketly.com/forum/thread/...response-code/

Thanks to RolandCP for the hint.