Insync Causing a "requires installation of untrusted packages" Error

When I went to update my software packages on Ubuntu 16.04 I was getting an Error saying "requires installation of untrusted packages".  After some investigating, I found that my Insync Key was showing Expired.  To fix this I ran the following commands in Terminal:

sudo apt-key remove ACCAF35C
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys ACCAF35C sudo apt-get update

This fixed my problem and let my Software Updates run.  

To figure out which KEY is expired run the following command in Terminal:

 apt-key list

This will display all your KEYS and you can look for the expired one. Or you can run:

apt-key list | grep “expired:”

Which will just show EXPIRED Keys.

Here's an article which explains it all better than I can. ARTICLE.