Comment 2 for bug 1081061

I solved this problem doing this:

'Applications' -> 'Software center' -> 'Edit' menu -> 'Software Sources...'

so click on tab 'Other software' -> 'Add' button

add the following line

deb http://packages.medibuntu.org/ precise free non-free

close Software Center and go to Terminal and execute the following lines

sudo apt-get update
sudo apt-get --quiet update
sudo apt-get --yes --quiet --allow-unauthenticated install medibuntu-keyring
sudo apt-get --quiet update

if no errors found, you can try

sudo apt-get install ubuntu-restricted-extras non-free-codecs libdvdcss2 faac faad ffmpeg ffmpeg2theora flac icedax id3v2 lame libflac++6 libjpeg-progs libmpeg3-1 mencoder mjpegtools mp3gain mpeg2dec mpeg3-utils mpegdemux mpg123 mpg321 regionset sox uudeview vorbis-tools x264 arj lha p7zip p7zip-full p7zip-rar rar unrar unace-nonfree vlc

works for me!
[ sorry for my poor english :( ]