php mysql авторизация - подскажите

Warning: Cannot modify header information - headers already sent by (output started at /login:8) in /login on line 51
Warning: Cannot modify header information - headers already sent by (output started at /login:8) in /login on line 52
Warning: Cannot modify header information - headers already sent by (output started at /login.php:8) in /login on line 55

вот эти строки:
# Ставим куки
setcookie("id", $data['user_id'], time()+60*60*24*30);
setcookie("hash", $hash, time()+60*60*24*30);

# Переадресовываем браузер на страницу проверки нашего скрипта
header("Location: check.php"); exit();