Will. I never liked Gmax or to be more accurate it doesn't like me.

I did experiment with it when FS2002 was first released & know the basics for both FS2002/4 & CFS2. First - make sure you installed the Gamepack files correctly as described in this topic.
http://www.simviation.com/cgi-bin/yabb/YaBB.cgi?board=airc;action=display;num=1037563242I tried exporting the default Dash 8 first. This was successful in both FS2002 & CFS2 & I posted shots at the time to prove it. The Gmax source files for the Dash 8 & the 2 other default AI only aircraft are included in the FS2002\gmax\Samples\Aircraft folder. You will find sample AIR file + Aircraft.cfg for most types in the FS2002\aircraft\templates folder. These will need renaming & editing appropriately for use in your project.
Export problems can be caused by all sorts of things. These very often give the error message you describe even if the Gamepack is correctly installed. Check out the most common ones here.
http://thegreatptmd.tripod.com/exporter/expoerror.htmAlthough originally developed for use with CFS2 I found that using MiddleMan from the same site makes export easier for both sims.