That paypal module I think it not compatible with Prestashop 1.6 because it's using order-confirmation.php file and this file is deleted on PS 1.6.

I think the module will be updated soon...

Anyways, have a look on Prestashop 1.5 and create the same file: order-confirmation.php


<?php

require(dirname(__FILE__).'/config/config.inc.php');

Tools::redirect('index.php?controller=order-confirmation'.((count($_GET) || count($_POST)) ? '&'.http_build_query(array_merge($_GET, $_POST), '', '&') : ''), __PS_BASE_URI__, null, 'HTTP/1.1 301 Moved Permanently');




Good luck