This error can potentially have many causes. These are causes that Wall Worm is currently aware of.

• You have set the $concave setting for the collision model but there are elements of your mesh that do not have unique smoothing groups.
• The hull has Open Borders. This most often happens when a model is imported into Max and some of the vertices are not welded. Simplest solution is to select the hull, go to vertex sub-object mode, select all vertices (CTRL+A) and click the Weld button in the modify tab. Then re-export the model.
• See the Prepare CM and Process CM functions of the Collision Hull Rollout.