Try installing libdvdcss2 like the message is advising you to do.
libdvdcss is the decoder that allows you to access css-encrypted commercial dvds. It's legality is dubious in some areas though.
By the way, it usually helps to post ALL the relevant information about your problem, such as the distribution you're using, the program you're using and the exact commands you've tried. I suggest reading the first link below in my sig. ↓
Last edited by David the H.; 08-01-2010 at 05:01 AM.