Finally I had the time to check your server.
My findings are that your provider is blocking the fetch of remote PHP code. As soon as it finds the string "<?php" it denies the request, it seems.
Thus your provider must use a firewall or content-based filter proxy, or tools like mod_Security, that block the call(s).
Sadly this means you have to convince your provider of disabling this, or you cannot use Spartacus.
The upside of your providers method is, that you can't easily be hacked by other people loading PHP-Trojans onto your site.
Best regards,
Garvin