hello friends! I have a small problem by exporting one unit: some polygons disappear and are not shown in the model exported. to know that is? the model is a single mesh.

Thanks again for your help.

some of your polies may be pointing the wrong way (they are inverted) easiest way to tell is to press U (polygon raycast select assuming you are using xsi) and try to select the polies that disappear, if you cannot then they are inverted. You can also turn on the polygon normal display and look at where the little green lines point to see which way the face of the poly is pointing.

well there are some ways:
1. little polys
2. square littles
3. inverted

solved ways:
1. triangulating poly
2. welding with other
3. removing it and trying other put on his place
4. inverting poly if the problem was the 3)

Spanish:
bueno me paso con varios clones es porque los polygonos son muy pequeños o son cuadrados y pequeños o tambien porque pueden estar invertidos entonces podes:
triangularlo, subvidirlo en mas polygons, borrandolo y tratando de usar otro para reemplazarlo

If you have too many polygons close together the munge will weld those verteces, making them appear as holes in-game.