ok so the line with the error is:
if (true && ((sizeof($this->Items) > 0) && ((isset($_SESSION['PromoCode'])?$_SESSION['PromoCode']:"") == "$_SESSION['PromoDiscount']"))) {
My guess is that it should be:
if (true && ((sizeof($this->Items) > 0) && ((isset($_SESSION['PromoCode'])?$_SESSION['PromoCode']:"") == $_SESSION['PromoDiscount']))) {
it looks like you had extra quotes around one of the values.