Comment 5 for bug 349355

I found a solution at:

https://answers.launchpad.net/ubuntu/+source/update-manager/+question/65788

What I did:
In a terminal, enter:
sudo gksu --desktop /usr/share/applications/software-properties.desktop /usr/bin/software-properties-gtk

Then I switched software sources from US to main

Then, in the terminal:
sudo apt-get install -f

update manager now seems to work.

Would anyone mind explaining what happened?

Thanks.