500 server error is almost usually due to a poorly configured .htaccess or a badly configured php.ini file. The owner of the site should have noticed it and be able to roll back to what he just did to cause it.
If you want to see a virgin website ban then try looking at thepiratebay.se and you will see what I mean.
Does look like a badly configured website. My guess is that you tried to access something that the owner wants to keep secure and he has some "special" error handler to replace the standard and this is faulty. So you hit the locked resource, the server issues the 403, the custom code intercepts it and breaks.
Site owners often like custom error handlers to make the site look better, provide more information and contact information.
If you do what you've always done, you'll get what you've always got. Jim Elliot
I work for Virgin Media but respond here on an individual basis. No comment or assistance offered is done in any official capacity.