"Your connection is not secure"? Can't log into Norton acct

My previous version of Norton Mobile had expired & I kept getting the "Your connection is not secure" error when I tried to log into the app to update to the new code I have.  The rest of the error message states "Cannot verify the server certificate. To protect your information, we have terminated the connection."  Out of frustration, I even deleted the Norton app, then went to Google Play & installed the latest version (3.17.0.3200) -- still get the same result.  I do have a password encrypted connection to my wifi router -- do I need to do something else?  The phone is a "Moto E (2nd Generation) with 4G LTG" running Android v5.1.

I note that I have another, similar phone that doesn't show this problem (a Moto G, also running Android v5.1) -- I'm able to log into my Norton account thru the app just fine.

I suppose I could try try the "Norton WiFi Privacy Secure VPN" app, but I'm hoping to avoid fooling around with that.

Thank you.