SagePay not returning confirmation

-- HikaShop version -- : 2.6.2
-- Joomla version -- : 3.51
-- PHP version -- : 5.5.31
-- Browser(s) name and version -- : Chrome 49 Mac
-- Error-message(debug-mod must be tuned on) -- : Forbidden
You don't have permission to access /sagepay_4.php on this server.
Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

After upgrading from Hikashop 2.5 to 2.6.2 we get the following error message when making a transaction.

"Forbidden
You don't have permission to access /sagepay_4.php on this server.
Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request."

This is at the end of the payment process and according to SagePay the transaction was successful. Screenshot of SagePay settings attached. Have the success/failure URL's changed?

Regards
Tj

just checked and the files sagepay_4.php (644) does exist at the root of the server and the files contains:

<?php
$_GET['option']='com_hikashop';
$_REQUEST['option']='com_hikashop';
$_GET['tmpl']='component';
$_REQUEST['tmpl']='component';
$_GET['ctrl']='checkout';
$_REQUEST['ctrl']='checkout';
$_GET['task']='notify';
$_REQUEST['task']='notify';
$_GET['notif_payment']='sagepay';
$_REQUEST['notif_payment']='sagepay';
$_GET['format']='html';
$_REQUEST['format']='html';
$_GET['local']='en';
$_REQUEST['local']='en';
$_GET['notif_id']='4';
$_REQUEST['notif_id']='4';
include('index.php');

Thanks for that, the old plugin works well.

Regarding the new Sagepay plugin, would specifically allowing access to sagepay_4.php in the .htaccess file prevent the problem? By default everything is blocked at the root of the site apart from index.php

RewriteRule ^sagepay_4\.php$ - [L]

Just a thought, I will update this post once I have had chance to test it.