How to fix software update error in ubuntu 12.04 LTS

Hello,
I have been using VLC on Ubuntu for some time now. Recently I saw that the program is becoming slow to load files and that is why I thought of updating it. I got the online updates from the official website and tried to do the update but I ran into the error below. So I thought that since update is not working, I could leave it the way it was. The next time I turned on my computer the same error showed up. What could be the remedy for this?

Error: Requires Installation of untrusted packages. This action would require the installation of packages from not authenticated sources. Libvlc5 libvlccore5 vlc vlc-data vlc-nox vlc-plugin-notify vlc-plugin-pulse
