Sagepay plugin, not getting to thank you page.

-- HikaShop version -- : 2.6.3
-- Joomla version -- : 3.5.1
-- PHP version -- : 5.6.22
-- Browser(s) name and version -- : any
-- Error-message(debug-mod must be tuned on) -- : Forbidden
You don't have permission to access /sagepay_2.php on this server.

Hi. The SagePay Plugin has stopped returning to the thank you page. Its getting the above.
I have tried making changed to the settings and saving. Tha payment is taken, but then the page errors.

Do I need to change the permissions of the sagepay_2.php file ? I have not had to before .

Many thanks