header() and passing sessions

I need some help passing a session variable with a header() function. According to www.php.net/header, the documentation states: *Note*: Session ID is not passed with Location header even if session.use_trans_sid <session.configuration.php#ini.session.use-trans-sid> is enabled. It must by passed manually using *SID* constant. so, I'm trying to manually pass the SID, but not having any luck. Here is a snippet of my code: There is a file login.php which has session_start(); and sets $_SESSION["username"] with the username you logged in with from index.php and has a form to click View Pending Requests which has the action of option.php. -- option.php -- <?php session_start(); if ($_POST["option"] == "View Pending Requests")

       {
       header('Location: http://intra.mdah.state.ms.us/helpdesk/viewpending.php?PHPSESSID='.session_id());
       }

?> --viewpending.php -- <?php session_start(); if (!$_SESSION["username"])

       {
       echo "You have not logged in";
       exit;
       }

?> so you click on View Pending Requests, and the URL in your browser is: http://intra.mdah.state.ms.us/helpdesk/viewpending.php?PHPSESSID=du75p41hel9k1vpuah799l2ce7 but viewpending.php says "You have not logged in". Why is that?