I see the issue now. There is a problem in the Medibuntu repository causing the error. The error is trivial, though, so don't worry about it, but I'll still release an update to the uberstudent-meta-restricted-extras package that fixes the error.
Workaround the issue for now by doing these steps :
1. Hit F12 on your keyboard to call a terminal and copy and paste this line in to it:
sudo apt-get update
2. Hit Enter on your keyboard and let it run until finished.
3. Now copy and paste this in to it:
sudo apt-get install -y cabextract chromium-codecs-ffmpeg-extra flashplugin-meta-uberstudent gstreamer0.10-ffmpeg gstreamer0.10-plugins-bad gstreamer0.10-plugins-bad-multiverse gstreamer0.10-plugins-ugly gstreamer1.0-libav gstreamer1.0-plugins-bad gstreamer1.0-plugins-ugly lame libdvdnav4 libdvdread4 libdvdcss2 mencoder openjdk-7-jre p7zip-full totem-mozilla totem-plugins unrar unshield vlc vlc-plugin-notify vlc-plugin-pulse
4. Hit Enter on your keyboard and let it run until finished.