Now in this version of Kontakt 6.6.1 (Bobdule) the 'add' button seems to be gone, and instead the 'manage libraries' thing takes you to the options where you'll see a list of your already installed libraries, and then a button to open Native Access in order to add or locate additional libraries.
Sorry for the stupid question, but up until now I have been using a previous version of Kontakt (either late 5 or early 6, don't remember) and back then adding a new Library was as simple as clicking 'add' on the main UI, locating the folder containing the nicnt (or generating it with library tool and then locating it), clicking on it and it would get added.
