Remove the installer slide show first:

• Go to Software center -> All files


• search for "ubiquity-slideshow"


• click on the Remove button


• wait until the Install button appears (this may take a while).

Or from the command line: sudo apt-get remove ubiquity-slideshow-ubuntu

The installer should work now.

Or, if you are installing Ubuntu Studio 12.04 LTS, for example :
sudo apt-get remove ubiquity-slideshow-ubuntustudio