I just formatted my pc… I installed it (as I usually do) and got this msg. 
I must say that my internet conection is good and running. I asume that’s an “out of date system” issue, because I never had it before.
Can anyone please help me here?
It is a known problem.
Just use the web-interface to login.
https://my.avast.com
Are you using a hosts file? It may have entries that can interfere. Read thru
https://forum.avast.com/index.php?topic=177548.0