Not sure, but I'm thinking that maybe an .htaccess file is causing a problem. I didn't see one in the cardtrix.co.uk directory, but, there may be one in the public_html directory that is causing a problem.

An easy way to check is simply rename it. You can rename it to something like htaccess (removing the preceding period) or .htaccess.bak. Once you do that, check it and if it works, you know it was something in the .htaccess file causing the problem. If not, you can simply rename it back to .htaccess and nothing is lost or changed.