That's puzzling as
http://www.promartsupplements.co.uk/blog//feed properly returns the XML data so it shouldn't be empty. If you have ssh access on your server what does this do?:
wget
http://www.promartsupplements.co.uk/blog//feed
If that can't download the XML and you can in a browser check with your host to see why you can't load local URL's.