I am trying to simulate a login scenario but when I run it via Nusphere I get the following messages

Warning: session_start() [function.session-start]: Cannot send session cookie - headers already sent by (output started at C:\websites\PHPTest\htdocs\myhelpdesk\CLM\IndexSecureUploads.php:4) in C:\websites\PHPTest\htdocs\myhelpdesk\CLM\IndexSecureUploads.php on line 20

Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at C:\websites\PHPTest\htdocs\myhelpdesk\CLM\IndexSecureUploads.php:4) in C:\websites\PHPTest\htdocs\myhelpdesk\CLM\IndexSecureUploads.php on line 20

Warning: Cannot modify header information - headers already sent by (output started at C:\websites\PHPTest\htdocs\myhelpdesk\CLM\IndexSecureUploads.php:4) in C:\websites\PHPTest\htdocs\myhelpdesk\CLM\IndexSecureUploads.php on line 32

My code is as follows

// nusphere complains about this so for debugging purposes I'll hard code the user for the moment
session_start(); // clm 12/04/08 create a server side session


if (isset($_GET['Logout'])) { // clm 12/04/08 log the user out
$_SESSION["user"] = "";
header("Location: $strLogoutLocation"); // clm 12/04/08
}
if (isset($_POST['frmUserNames']) || isset($_SESSION["user"])) { // clm 12/04/08 run the code if the username is set by login page or the session variable is already set
if ($_SESSION["user"] == "") { // clm 12/04/08 If the session user value has yet to be set do it
$_SESSION["user"] = $_POST['frmUserNames']; // clm 12/04/08
} // clm 12/04/08
} else {// clm 12/04/08 if the user hasn't logged in then go to login page
header("Location: $strLogoutLocation");// clm 12/04/08
} // clm 12/04/08
$user = $_SESSION["user"]; // clm 12/04/08

Obviously this is a pain as I use the $user variable as a KEY, surprise surprise.

Works fine on the server. Is there anyway that I can run this locally?

The error suggests that output was sent on line 4 of your script. For example, you are doing an echo or print. You cannot have any output before setting a cookie or sending a header.

I do not see the problem in your script source code around line 4. Did you paste the whole script?