This Connection is Untusted

I use Stockcharts.com and it works, but then I get this message below.  After a few minutes I can refresh, but it happens a few times a day.  How can I fix this:

This Connection is Untrusted

You have asked Firefox to connect securely to stockcharts.com, but we can't confirm that your connection is secure.

Normally, when you try to connect securely, sites will present trusted identification to prove that you are going to the right place. However, this site's identity can't be verified.
What Should I Do?

If you usually connect to this site without problems, this error could mean that someone is trying to impersonate the site, and you shouldn't continue.

Hi Gene,
For help on this issue please try disable scanning of TSL/SSL traffic:
Open AVG and click "Options" -> "Advanced Settings" -> "Web Browsing Protection" -> "Online Shield" -> "Expert Settings" Uncheck "Scan encrypted (TLS and SSL) network traffic" option.
Thanks

Hi Gene,
For help on this issue please try disable scanning of TSL/SSL traffic:
Open AVG and click "Options" -> "Advanced Settings" -> "Web Browsing Protection" -> "Online Shield" -> "Expert Settings" Uncheck "Scan encrypted (TLS and SSL) network traffic" option.
Thanks