Moneris Payment Module 1-24

I have installed the Moneris Payment Module 1-24 on Zen Cart version 1.3.9d. When a credit card transaction is Approved by Moneris the order completes successfully. However, if the transaction is Declined (response code > 49), the error message is not displayed. It my case a page not found, HTTP 406 is displayed.

Looking at the code in in the monerisselectplus.php script it looks like there should be a page redirect to the checkout_payment page with an error message. See the code below in bold text;

function before_process()
{
global $_POST;

	if ( (intval($_POST['response_code']) < 50) && (is_numeric($_POST['response_code'])) )
	{
		$this->moneris_order_id = $_POST['response_order_id'];
		$this->moneris_response_variables = implode(';', $_POST);
		return false;
	}
	else
	{
		**zen_redirect(zen_href_link(FILENAME_CHECKOUT_PAYMENT, 'error_message=' . urlencode(MODULE_PAYMENT_MONERISESELECTPLUS_TEXT_DECLINED_MESSAGE), 'SSL', true, false));**		}
}

If anyone has experienced a similar problem with this module and has found a fix I would appreciate your help. Thanks.