I had the same problem with TORCS (also, its level editor wasn't able to create AC3D file). Trackgen doesn't make any file no matter what arguments I use. When I just open the application, it list all arguments. When I use a specific argument, the list isn't shown, but no file is made. It doesn't work even with the tracks supplied with the game.
I'm using Speed Dreams 2 beta on Windows XP SP3.