single sign on

hi,

i have phprunner 6.2 build 16275 enterprise and i try to use single sign on but it doesn't work.
I put

if ($_SERVER["REMOTE_USER"])

{

$_SESSION["UserID"] = $_SERVER["REMOTE_USER"];

$_SESSION["AccessLevel"] = ACCESS_LEVEL_USER;

header("Location: menu.php");

exit();

}

in login page:Before process

but i always have the login page
if i try

echo "Your remote user: " . $_SERVER["REMOTE_USER"];

in login page:Before process
the variable $_SERVER["REMOTE_USER"] is empty

may someone help me?

thanks.