/efs error while trying to fix bricked phone

My Samsung Galaxy S III GT-I9300 wouldn't go past Samsung screen on boot, I had installed Resurrection Remix Mod by i'm not sure but i think it was CyanogenMod. Tried installing stock rom, couldn't get my head around it. Also while trying to fix this I started getting the error /efs when trying to get to recovery. What should I do?
Thanks in advance