it always helps to have the error message to refer to.
try changing this line:
<?php if ($totalRows_rsCoupondb > 0) && (isset($_SESSION['expDate'])) && (time() <= strtotime($_SESSION['expDate'])) { //
to:
<?php if (($totalRows_rsCoupondb > 0) && (isset($_SESSION['expDate'])) && (time() <= strtotime($_SESSION['expDate']))) { //