Really. THese error are usually created by the anti virus product you use.

Avast is one of a number of those dodgy anti virus products that scan your network connection by hacking methods. Interesting logic really they hack you so they can protect you from hackers.

The usual cause is the issuer in the message is someone like avast or some other organization that wants to be a certifying authority without outlying the cash to have themselves audited to become one. But only by examining the details can you determine who the issuer is so you know the root cause. The issuer is unknown to the chain of trust on which internet security is built is what the error is about, not that the certificate does not contain the issuers name.

The solution usually is to get an anti virus product that respects security instead of encouraging you to break it by routinely creating exceptions. But who is the issuer in this instance?

Thank you, but I use Kaspersky Internet security and I can't find where therin the problem lies David

I have it too, using Bitdefender. See attached screen shot.

This is the problem with Kaspersky. https://support.kaspersky.com/6851

This is the problem with Bitdefendar. https://www.bitdefender.com/support/what-to-do-when-security-certificates-cannot-be-verified-installed-1090.html

I just Googled those pages in under a minute. I did not read them in detail as I do not provide support for anti virus products.

https://support.mozilla.org/en-US/kb/troubleshoot-SEC_ERROR_UNKNOWN_ISSUER#w_kaspersky