We are using jQuery in our application. We have used a jQuery plugin to implement JavaScript session.
It is working properly in Firefox and most Internet Explorer 8
I had the very same problem recently. In my case on the top of a php script I had some code generationg obviously some extra output to the browser. Removal of empty lines (between ?> and html-tag ) and simple cleanup helped me out:
<?php
include('../config.php');
//
ob_clean();
?>
<!DOCTYPE html>