logout.php不会重定向到服务器上的目标页面，但可以在localhost上运行

I am trying to to understand why a simple logout.php script works on localhost but not on live server. Thanks in advance for any help.

here is the entire logout.php file

<?php//Start the session
session_start();

//Terminate the session
session_unset();
//Redirect users to login page
header('Location:  http://www.somewebsite.com/login');
exit(); 


?>