logout page error session

logout page error session

I'm having a little problem when I try to logout
<?php
session_start();
session_unset();
session_destroy();
header("location:../");
?>
this is my logout code, and that is the error:
Warning: session_start() [function.session-start]: Cannot send session
cache limiter - headers already sent (output started at
/home1/jota/public_html/adm/logout.php:1) in
/home1/jota/public_html/adm/logout.php on line 2
Warning: Cannot modify header information - headers already sent by
(output started at /home1/jota/public_html/adm/logout.php:1) in
/home1/jota/public_html/adm/logout.php on line 6