Durup dururken hata_Warning:Cannot modify header information

[limxona]

Merhaba arkadaşlar. Forumdan durup dururken bu hatayı aldım. nedeni ne olabilir sizce.Hiç bişe eklemedeim çıkarmadım hatta foruma ne uye olundu ne de mesaj yazıldı. Yoktan yere bu hata ne diye çıkar anlamadım.Ama sadece index.php de var başka yerde yok.

Bahsi geçen hatalarda sırasıyla şu kodlar var
sessions.php on line 371 : setcookie($cookiename . '_data', serialize($sessiondata), $current_time + 31536000, $cookiepath, $cookiedomain, $cookiesecure);

sessions.php on line 372 : setcookie($cookiename . '_sid', $session_id, 0, $cookiepath, $cookiedomain, $cookiesecure);

page_header.php on line 582
: header ('Cache-Control: no-cache, pre-check=0, post-check=0');

page_header.php on line 588
: header ('Expires: 0');

page_header.php on line 589
: header ('Pragma: no-cache');

Warning: Cannot modify header information - headers already sent by (output started at /var/www/vhosts/gurgula.net/httpdocs/forum/index.php:6) in /var/www/vhosts/gurgula.net/httpdocs/forum/includes/sessions.php on line 371

Warning: Cannot modify header information - headers already sent by (output started at /var/www/vhosts/gurgula.net/httpdocs/forum/index.php:6) in /var/www/vhosts/gurgula.net/httpdocs/forum/includes/sessions.php on line 372

Warning: Cannot modify header information - headers already sent by (output started at /var/www/vhosts/gurgula.net/httpdocs/forum/index.php:6) in /var/www/vhosts/gurgula.net/httpdocs/forum/includes/page_header.php on line 582

Warning: Cannot modify header information - headers already sent by (output started at /var/www/vhosts/gurgula.net/httpdocs/forum/index.php:6) in /var/www/vhosts/gurgula.net/httpdocs/forum/includes/page_header.php on line 588

Warning: Cannot modify header information - headers already sent by (output started at /var/www/vhosts/gurgula.net/httpdocs/forum/index.php:6) in /var/www/vhosts/gurgula.net/httpdocs/forum/includes/page_header.php on line 589