when creating the Bassed on session session variable value trigger for the rule, you added an extra space in the name of the session variable.
The code of the trigger is:
if (true && (((isset($_SESSION[' next_day_ship'])?$_SESSION[' next_day_ship']:"") == "1"))) {
it should be:
if (true && (((isset($_SESSION['next_day_ship'])?$_SESSION['next_day_ship']:"") == "1"))) {
see the following page for information on the cause and fixing the headers already sent error:
148/