[PLUG] Ubuntu MATE 16.04 Update Failure

[Dick Steffens]

I'm getting an error message when using "Software Updater"

I am presented with a long list of updates. I click "Install Now", type 
in my password when asked to authenticate, and then get a message that 
says, "Requires installation of untrusted packages. This requires 
installing packages from unauthenticated sources." I have two options, 
"Settings..." and "Okay". When I click "OK" the window closes and 
nothing else happens. When I click "Settings...", there's no obvious 
thing to change. It doesn't tell me which packages are from untrusted 
sources, so I can't skip those packages, or tell it to go ahead and 
install them anyway.

I tried the solution found at:

https://askubuntu.com/questions/635037/software-updater-warning-requires-installation-of-untrusted-packages?utm_medium=organic&utm_source=google_rich_qa&utm_campaign=google_rich_qa

It let the "Software Updater" process run most of the way, but then 
said, "Package operation failed. The installation or removal of a 
software package failed." And again the options are "Settings" and "OK" 
but no indication of which package raised the complaint. I clicked on 
"Settings" and clicked through each of the tabs. When I closed that 
window the "Software Updater" window returned with the same long list. I 
clicked "Install Now", authenticated it, and it failed again.

Any recommendations on how to figure out which package is causing the 
problem?

Thanks.

-- 
Regards,

Dick Steffens