header() and passing sessions

[Adam Williams <awilliam@xxxxxxxxxxxxxxxx>]

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?