You will need to complete these steps while logged in on your Chromebook. It will take approximately 10 minutes.
Click on this link to download the Chromebook security certificate. 2048-SHA256 Certificate
Click on the time in the bar at the bottom of the screen.
Click on "Settings"
Scroll to the bottom of the page and click on "Show advanced settings"
Scroll down to "HTTPS/SSL"
Click on "Manage Certificates"
Click on "Authorities"
Scroll to the bottom. You may see two certificates with Zscaler in the name. They should have "Untrusted" in front of them. This is causing the problem. If you don't see the untrusted certificates proceed to step 12.
Click on one of the "Untrusted" buttons. Click "Delete". Click "OK" to confirm the delete.
Repeat the step above for the second untrusted certificate.
Click on "Import". A window opens to show downloaded files. The two certificates you downloaded in steps 1 and 2 should be there.
Click on the certificate named ZscalerRootCertificate-New.crt
A "Certificate Authority" window opens. Click on each of the three boxes to add check marks.
You should now be able to access Google sites with no error message.