Make sure you moved that file named "items.cfg" to the main Feral Heart folder (The FHRoot folder if you're on a Mac) and clicked replace when it asked. Also, make sure you moved the individual items into the items folder, not the folder itself.
For what? You put the items.cfg file into the main Feraleart folder, not the items folder if that's what you were asking. Also, for the items, move them all individually, not the folder they come in. You don't want a items folder in the items folder. x3