@crazydragon
Can you be a bit more specific about the error you get on export.
Most of the problems I have found or fixed for others tend to be problems caused by:
1) unattached verts
2) models created by attaching polies to meshes
3) models created by attaching instances to meshes
4) meshes attached to meshes with different uvw's
But usually you can get around these issues, and the biggest pain in the butt is when you've gone on to bone, skin and animate the model before realising you messed up.
So rules of modelling are:
1) Save regularly - I average about 20-50 interim versions on a complex model so at worst I might lose 10-20 minutes work.
2) Everytime you save, run the export script - waste 2 minutes running a clean export or.....
3) When you attach parts of the model check it has done what you thought it should do. The best indicator I have found is the texture. If you call up the entire textures and more than one texture is assigned to an object you've got problems!
4) Make sure that you reapply the base model texture before exporting.
5) Make sure that when you convert the .3dx file to .brg you use the exact model you used for the .gmax base.
.... and I think to myself; what a wonderful world ... yeh!!!