Are you trying to rip a dvd but you're don't open a dvd? Probably you need a lib that decrypt the dvd. See this instructions:
Installing libdvdread on Ubuntu
Install the libdvdread4 package (no need to add third party repositories) via Synaptic or command line: (note: if you have installed *ubuntu-restricted-extras this has already been installed automatically for you)
open a terminal (alt+ctrl+t)
so, in the terminal, type:
sudo apt-get install libdvdread4
after installing,type:
sudo /usr/share/doc/libdvdread4/install-css.sh
Installing libdvdcss on Ubuntu
open a terminal (alt+ctrl+t)
then, type:
wget ftp://ftp.videolan.org/pub/debian/videolan-apt.asc | sudo apt-key add -
echo "deb ftp://ftp.videolan.org/pub/debian/stable ./" | sudo tee /etc/apt/sources.list.d/libdvdcss.list
sudo apt-get update
sudo apt-get install libdvdcss2