If you have a valid purchase code then this error means for some reason your server is unable to reach hostingbilling.net

You can get around this error by changing the server URL the installer is trying to reach

To change the URL please follow these steps

In the files that you uploaded open application/config/

Edit the file named constants.php

In line number 30, change this:

define('UPDATE_URL', 'http://hostingbilling.net/');

To this:

define('UPDATE_URL', 'http://updates.hostingbilling.net/');

This should allow you to continue and if it doesn't please send an email to support@hostingbilling.net for quick assistance.