Error 501 (net::ERR_INSECURE_RESPONSE): Unknown error is an error you get in chrome when you view a page with an iframe that loads a HTTPS page with an invalid SSL certificate. If you find HTTPS page on the same domain that is not in an iframe you will get the standard red page saying the site is unsafe. If you click procceed the page will load as normal. You can now go back to the page with the iframe and browse normally.

If you are not a developer or are not sure why the SSL certificate is invalid then DO NOT CLICK the button to procceed.