During the model creation and development process certain model files may become corrupt.
Beware!
Model files become corrupted for these reasons:
Quote
GeosetAnims that do not point to a geoset (ie no 'GeosetId' line).
Dodgy extents -- negative maxes and positive mins (beware when editing the Marine and Tauren).
Team-colored particles (when not modified from an existing emitter).
Animations which last 0 seconds.
Lights when attached to root bone (only sometimes).
Certain texture animations (if not done properly).
Polycount (if higher than 100000).
Faulty Ribbon Emitters.