Noob question: I'm following & enjoying the tutorial at https://learn.adafruit.com/ktowns-ultimate-creating-parts-in-eagle-tutorial/introduction & the following pages, but am stuck in the device editor. My newly created package is visible in the 'Create New Package Variant' dialog, but it's greyed-out and cannot be selected. Any clues as to what I've got wrong would be gratefully received.