This error is usually caused by models having a $concave flag that do not have proper collision hulls.
Using WWMT in 3ds Max to create your model's collision hull with the Quick Hull feature.
The Collision Model & Physics rollout in WWMT. Assign a collision hull, create a hull with the Quick Hull function and use advanced features such as the Convexity Hull Wrapper.
Articles about making collision models.
Use Wall Worm to quickly build convex collision hulls for your model.
How to export brush geometry with the Wall Worm VMF Exporter.
Archive of Wall Worm Version 1.X changelog in 2011 through 2014.
Archive of Wall Worm Version 2.X changelog in 2014 through early 2017.
When exporting grouped models to SMD, the SMD exporter will fail to export your model correctly.
ShellVex is a scripted geometry plugin for 3ds Max that allows you to create convex geometry blocks from the polygons (or tris) of other objects in the scene.
Many of the projects and services provided by Shawn Olson are done in his spare time. If you love Wall Worm, you can show appreciation with a donation.