Esper: There are many good reasons why 3D engines normally don't use a data exchange format like FBX, 3DS, or OBJ for their models, but a special model format, such as MDL.

I guess you already learned one of them: If there are any FBX import problems, you want them to happen during game development, and not during gameplay on your end users' PCs.

Other reasons why a proprietary model format like MDL is superior to FBX: It loads much faster, has less overhead, needs no import library, and has more features such as LOD stages and surface shaders.