This error is encountered when the request that was sent was evaluated as problematic by our firewall. If this error is displayed, contact our support, that will give you additional information.
If you get the error 466 when you are loading a website hosted with us, it means the the HTTP request you sent was evaluated as problematic by our firewall which blocked it. This firewall serves mostly to protect your website against various attacks. A default example of the blocked request is a brute-force attack trying to authenticate to WordPress (e.g. via xmlrpc API).
Error 466 is also interesting because the number is specific to our infrastructure. That means HTTP Response 466 from the website, that is not on our servers, may mean something completely different than with us.
Of course it may happen that our firewall blocks a legitimate request. In these cases the request has been blocked, because it is located in the external database, that we use for rule creation for our firewall. The solution is either to rewrite the request from your side or contact our support, that will help you find the most suitable solution.