Why appears "Certificate Error" in some blocked websites?

That message appears since you are trying to open a blocked website, using a HTTPS secure connection. So the Browser informs you that the certificate has not been realeased by a reliable/recognized authority. It's possible to avoid this error by installing our Certification Authority on your internal devices. Here below the guide: CA installation guide Alternately, in most cases, you can click Proceed anyway to force the site to open. In this case you will see the Filter blocked page.