Not updating

Hello all, I'm new to the forum, but have been using Pinguy 12.04 64 bit for just over a year now. Other than a few minor tweaks and learning issues, it's worked very well for me.
My question: over the last few weeks, the auto update keeps telling me that the "list of packages could not be refreshed", particularly anything with medibuntu in the name. Is this just a setting that needs to change? Thanks in advance for any help.

rickhen