Comment 43 for bug 883585

Antonio, your problem is that under Kubuntu the printer's firmware file does not get automatically downloaded onto your computer. This will be most probably fixed in Ubuntu Precise (12.04). See also bug 913730. For the time being run

sudo hp-plugin

in a terminal window and follow the instructions on the screen to get HP's driver plug-in (which contains the firmware files) installed on your system.

If the command above does not work, run

sudo apt-get install hplip-gui

and then run the command above again.