Https credentials in google chrome

I get the error “NET::ERR_CERT_INVALID” in google chrome in some https sites.

Common Name (CN)	Avast Web/Mail Shield Root
Organization (O)	Avast Web/Mail Shield
Organizational Unit (OU)	generated by Avast Antivirus for SSL/TLS scanning

The file id is R94BP.
Do I need to add some more info? Is there a way to disable that Https protection thing or what does it do anyway?
How can I know that some website is that really website if I cant match the credentials to the original credentials? In different browser or pc I get different credentials for that website.