Safari cannot open page-address is invalid

Hello,

This means that you are attempting to access a website that is either non-functioning or you entered an invalid website address.

I presume that most websites that you access are rendering as normal in your web browser.

If so, it is perhaps possible that the URL that you are attempting to access has been blacklisted due to being compromised. If the target website URL is hosting malware, or other serious compromise - for your protection, your DNS provider / ISP may have blacklisted or sink-holed the bad URL/site.