sites.google.com normally uses encryption to protect your information. When Chrome tried to connect to sites.google.com this time, the website sent back unusual and incorrect credentials. This may happen when an attacker is trying to pretend to be sites.google.com, or a Wi-Fi sign-in screen has interrupted the connection. Your information is still secure because Chrome stopped the connection before any data was exchanged.
You cannot visit sites.google.com right now because the website uses HSTS. Network errors and attacks are usually temporary, so this page will probably work later.