W: The repository 'http://download.fpcomplete.com/ubuntu yakkety Release' is not signed

Solution 1:

When I visit that repository in a web browser, I get only the same Access Denied message. If the site is still being run as a software source for Ubuntu, then the server appears to be misconfigured.

This repository isn't listed in /etc/apt/sources.list but apt-get is using it when you perform the update action. This means that it is listed in a file in the /etc/apt/sources.list.d folder instead.

You can find and remove/rename this file in a terminal, if you like, but you don't have to. You said you changed your Ubuntu mirror in Software & Updates from "Server in South Africa" to "Main Server." That's in the Ubuntu Software tab in Software & Updates. Since that didn't affect this particular repository, you can expect that it will be listed in the Other Software tab instead.

^{My Other Software tab in Software & Updates. (I'm running Xenial rather than Yakkety.)}

You can then uncheck the entry for http://download.fpcomplete.com/ubuntu yakkety, and you should be able to run sudo apt-get update without problems.

Solution 2:

I installed and ran y-ppa-manager and that did the trick!

sudo add-apt-repository ppa:webupd8team/y-ppa-manager

sudo apt-get update

sudo apt-get install y-ppa-manager