Is this happening all the time or only when you try to visit certain sites?

Normally, this is down to a setting in your browser, nothing to do with the search engine. When you visit an HTTPS website, the browser checks that the site's certificate is up-to-date and valid. If the browser encounters a problem with certification it will display that message instead of loading the site.

It's a normal security measure included in every browser to keep you safe and, as such, does not need fixing.

Hope that helps.,

Jim