Comment 3 for bug 212249

It appears that dpkg (a tool which is responsible for installing packages on Ubuntu) was interrupted at some point, which messed it up a bit. There are any number of reasons why it might have been interrupted. You might like to try the following:

Open a Terminal (Applications -> Accessories -> Terminal), type the following, then press the Return key:

sudo dpkg --configure -a

Enter your password when prompted and press Return again. Follow any instructions on screen.