on the standbyconfirm.php and customer_login.php pages you have the following code:
<?php
if (!session_id()) session_start();
if($_SESSION["standbyClassID"] < '1') {
$_SESSION["standbyClassID"] = "".((isset($_POST["classid"]))?$_POST["classid"]:"") ."";
}
if (!session_id()) session_start();
if($_SESSION["standbyInstanceID"] < '1') {
$_SESSION["standbyInstanceID"] = "".((isset($_POST["inid"]))?$_POST["inid"]:"") ."";
}
?>
this is probably resetting the sessions because the form POST will not exist on these pages.
you should only be setting the sessions on the class.php page not the others.