1amg0d

hi, im kinda newbie to the whole fix it thing with ftb but since i updated to 1.7.9 in reg minecraft my ftb wont allow me to get into any servers. it is telling me that ID 7 is mismatched between world and game and i dont know how to fix it. Can some1 give me somewhat detailed steps on how to fix? i dont no how to copy the config folder over either.. i couldnt find it in my ftb folder..