Hmm...the only thing that comes to mind is the installer. I think to install the full version of Nat3 you'd have to run an actual "Setup" variant (as opposed to an "Update" variant). I'm not sure what your history with the plugin is but it's conceivable if you have upgraded from a previous version maybe that process (the Nat installer) has never been run?
If you have your license handy you could try to uninstall-reinstall and make sure to use the Nebula3Pro Setup installer (it should be available in your downloads on the site here). That will blow your authorization away, though, so if you don't have that handy you may want to dig it up first.