Sessions not working in IE

I have an admin site that stores a session in a folder using the following:

ini_set("session.save_handler", "files");
session_save_path ("tmp");

ini_set("session.save_handler", "files"); $_SESSIONusername? = $username;

header("Location: main.php");

Then I check the session with this:

function validSession($username) {

if (!isset($_SESSIONusername?)) {

$_SESSIONstatus? = "You must login"; header("Location: logout.php"); exit;

}

}

Everything works fine I can add text to the WYSIWYG and use every tool in the editor but as soon as I press the image button it destroys the session and when I press submit or refrech the page it logs me out. This only happens in IE not firefox or Chrome