Attention to those who use the testing PPA (if you installed retroarch after dec/16/2014 disregard the information) Attention to those who use the stable PPA (if you installed retroarch after jan/10/2015 disregard the information)
Purge all your cores, make sure you don’t have any info file added manually to the /usr/share/libretro/info/, and then install all your cores again.
sudo apt-get purge libretro* sudo apt-get install libretro*
Info files are not coming any more with each core package, there is a package now with all this info: libretro-core-info. So you need to purge all cores first and reinstall them, because the old cores in the system have the same file of this new package. Sorry for the inconvenience, this change was inevitable.