This error is found if,
Check your default sources.list for any URL(s) starting with https, change them to http if found,
Next check for any additional sources defined in "/etc/apt/sources.list.d"
Edit them and check for any URL(s) starting with https, change them to http if found.
Once you've found any https URL(s) in your sources and changed them to http, run apt-get update,
Next, install the method driver /usr/lib/apt/methods/https,
apt-get install apt-transport-https
Once this is done, you can change back any URL(s) in your sources to https and then run apt-get update again without any issues