Ubuntu 12.04 - Installing and registering a DVD decryption library

I couldn't open any DVD... this fixed it. Run the following two commands on terminal. Don't worry if the first step tells you that you already have the library, as the second step registers it properly.

sudo apt-get install libdvdread4

sudo /usr/share/doc/libdvdread4/install-css.sh

Reference, source:
http://askubuntu.com/questions/109103/how-do-i-install-a-dvd-decryption-library