If you haven't changed any of the views that are installed with the GTD add-in, then reinstalling will likely be your best bet. My guess (and reiterating that I don't know how the GTD product works specifically) is that the setting that indicates GTD is there is located in a different place from the GTD installation itself, and Outlook is picking up one but not the other.

Note: Usually, reinstalling a product on the same computer for your own personal use is legal, but you should double-check the GTD user license to be sure before trying to reinstall.