I would guess the model has shapes in it SMedit doesn't like and you will need to use a 3D modelling program to clean it up to be compatible with smedit. Maybe try opening it in something like Blender which is free, and re-exporting it. Also check the model for any errors in the programs before exporting them.
Some models can do different shape polygons on the model and some programs like them a certain way, e.g they may not like triangles and need quadrilaterals to function correctly. Also if a model has holes in it, SMedit can spaz out, especially the hollow function, as it will not be able to tell the inside from the outside.
In these kinds of cases I'd recommend doing a web search. Lots of info on these kinds of things out there