Can't see anything wrong there at first sight (from RC2 on, you should replace the
GetPlugin function with a new macro found in the SDK, but for the time being, that's fine).
Do you have __GNUWIN32__ WXUSINGDLL BUILDING_PLUGIN defined as compiler options?
And (very obvious thing) do you have the plugin copied to the plugins folder and enabled it in plugins settings?
What happens if you move the INT 3 into the constructor, does that crash the application on startup?
EDIT:As a sidenote,
wxBell(); will let you know that something happened, too, and is a little less intrusive than
INT 3