I'm running a fairly vanilla 14.04 Ubuntu on a newish HP desktop. Just yesterday I got the dreaded "Failed to download repository information":
A screenshot of this window has been seen on AskUbuntu before. I have checked related threads here, and also looked at a helpful off-site article. The strange thing now is that when I run
sudo apt-get update I get back
E: Invalid operation update, so I can't even work out what the offending PPA is.
The Updater does find updates and apply them (you can see what I got today if you like), but that's little help in diagnosing the problem.
So my question: how do I fix this?!