These errors likely have nothing to do with your computer. They have to do with the security certificate on the web server you are trying to reach. Most of the time, these are not harmful and just mean exactly what it says. The web server administrator needs to update the certificate.
However they can be an indication of a bad web site. Thus if you tell me the complete address of the web site you are trying to reach, I will take a look. I'm looking for the full address in your address bar of your browser that would look something like:
Hi. I'm just checking in to see if your issue has been resolved. Are things working OK now?