@toppy,
About the firewall rules, when you delete the rules they are re-created again when the specific program wants to connect.
In some situations, when a program is updated (like Avast just was recently updated to a new stable version), the firewall is not 100% that the "old" program is the same as the new. So the firewall denyes the connection.
By deleting the rules (if the firewall is configured correctly, then) it should ask you again for permission when Avast tries to update.
For some reason (and I can think of several), your definitions date is currently not "in sync".
My suggestion would be to delete the firewall rules, reboot, wait for about 10 minutes after the reboot and review the information (Avast main GUI -> maintenance -> update). Please review the info there, but don't force the update.
There are additional steps possible, if that is not enough. Please report back.