We had an issue recently where there was some difficulty contacting the paypal server to verify an IPN passed back to a PrestaShop store.
The v1 Final version of the paypal validation.php file only uses fsockopen to establish an http connection to paypal (production or sandbox) to verify, so we've added a little code to ours to:
- Use a secure connection if possible (using fsockopen)
- Use cURL if the above fails to connect, and
- Use an insecure http connection if the above fails.
The patched files can be downloaded here: Paypal module update for Version 1.0 Final