xml's prevent Access from working correctly and must be deleted if present.
One word of warning, and it took me 3 days of troubleshooting with absolutely no constructive help from NI, do not under any circumstances run the old Service Center during the process (mine opened at some point during the Kontakt re-install) and it cause me major headaches with Native Access - some library's were showing as demo only and a lot said they were installed and they weren't showing in Kontakt (with no way to install them) - the old service centre. There's an article on NI somewhere (or as has been said it may have been an post here) about how to do it but yes basically you install pre 5.6 Kontakt (or earlier, basically last version before Native Access came into being) and add your non-Native Access libraries with the 'add library' button, then fire up Native Access, set your NI install path in the prefs and it will then pick up all your other NI installs and Kontakt libraries and authorise them. I did a complete clean install of my studio rig a couple of weeks ago.