ProtX are making some chganges to their IP address range, so if you use ProtX please
To check if your site is using the correct URL, simply download and open /includes/modules/payment/protx_*.php (there might be one or there might be two). Make sure that the URL being used in each begins with http://ukvps.protx.com
Easy as 123. If you need this checking, I can do so for you – email me on oscshops AT gmail DOT com