Can't change software sources via GUI following upgrade to 17.10 (using Gnome)

[Kaj Haulrich]

On 22-11-2017 14:59, Colin Law wrote:
> Having upgraded to 17.10 (from 17.04), when I open Software and
> Updates I am unable to select or deselect s/w sources. I do not get
> the popup asking me to enter my password.  I do not see the problem on
> another machine with a fresh install of 17.10.
> 
> Any suggestions where I might look to sort it? No success searching
> Google and Launchpad.

The easy way: You could install synaptic and manage your sources from there.
or the nerdy way:
edit /etc/apt/sources.list (as root, of course).