It doesn't recognize an FSDT airport, if you modified the name of the AFCAD that comes with it, and renamed it.
In that case, it will still work on it, without any customization, but will be treated as if it was any other airport, which means it would require purchasing GSX.
This, assuming that with "doesn't work" you mean that you saw the Trial message on an FSDT airport. If, instead, you meant something else, than it's an entirely different issue, which is best to explain better.