[ubuntu] 16.04 LTS "Failed Download Repository Info"

My recent install Ubuntu 16.04 LTS on 3 completely different systems (1 Atomx32, 1 Intel 2708x32, 1 Intel C2Dx64). I get a notice - "Important OS and App Softw Updates Available". Then it "Kindof" updates, but first I get the msg "failed to download repository information". then I click OK and it does retrieve some files. My i-net service is working perfectly. Initial install from ISO DVD and initial massive OS updates went smoothly. Finally, it does report "software on this computer up-to-date".

I used the following commands:
sudo apt-get update (found several hundred kb files failed to download a ppa launchpad)
sudo apt-get upgrade (several new packages)
sudo apt-get dist-upgrade (zero results)

The Ubuntu Software Updater is one of the most reliable and admirable aspects of my recent several years of using v12>v16. Up until now I've never had a problem. So what has changed? Should I be worried important security patches will be missed? How can I correct this "Failed Download Repository Info" state? What does this mean? Is this message merely pertaining to a single ppa app that can't get updates?

My guess is I have an obsolete ppa app that is not listed in the synaptic inventory. So if I was able to install it in the first place, they must have chnged their repository location since then, right? Is this normal? Security Risk? Is everything else OK?

I think I know what the app is, but this "failed" msg is still scary. Error msg needs to be more specific.