Can't store sessions

[Mr_Alien]

Hi, I am getting an error when trying to store a session variable.
I am new to sessions, so I am puzzled.

I am using the following script as an example only:

<?php
header("Cache-Control: no-store, no-cache, must-revalidate");
header("Cache-Control: post-check=0, pre-check=0", false);
header("Pragma: no-cache");

    session_register("s_username");

    $s_username = "administrator";

header( "Location: members.php" );

?>

and I am getting the following error message:

Warning: open(/tmp\sess_c4646058ed1d24aef16bd16fbe75061c, O_RDWR) failed: m (2)

which fails on session_register line.

Please help!!! Thanks

[LordShryku]

I don't see you calling session_start();

That may be your problem.

<?
session_start();
header("Cache-Control: no-store, no-cache, must-revalidate");
header("Cache-Control: post-check=0, pre-check=0", false);
header("Pragma: no-cache");
session_register("s_username");
$s_username = "administrator";
header( "Location: members.php" );
?>