I've been having this annoying problem lately since I upgraded from Linux Mint 9 to Ubuntu 12.04. It started when I was installing VLC from the Ubuntu Software Centre a few weeks ago. I kept getting this error with packages with "Size mismatch". This happened with many other programs later on. I just got around it by downloading the packages separately and installing them that way. Now I get two updates for packages I installed in that manner. I tried changing from where I download the packages, it didn't change anything. If anyone can help me with my issue it would be splendid. Screen shot below: http://i1078.photobucket.com/albums/w499/Nammi-namm/Screenshots/Screenshotfrom2012-07-02035645.png