invalid certificates

I would like to know how to keep Avast! from blocking so many sites I try to view. I keep getting messages telling me Avast! has blocked this site because the following certificate is invalid ! This happens to 3/4 of the sites I try to view ! Most of which I know to be safe ! There has got to be a way to deactivate this behavior ! Please ? Thank You !

What exact avast version ?
What browser/version ?
Does it also happen with other browsers ?
What sites ? (give a few examples)

This happens to 3/4 of the sites I try to view ![b] Most of which I know to be safe[/b]
How do you know?

Safe today can be hacked tomorrow

Every 3.6 seconds a website is infected > http://www.scmagazine.com/every-36-seconds-a-website-is-infected/article/140414/