Here is a collection of known issues with Wall Worm, 3ds Max and/or the Source Game Engine.
Sometimes WW Pro will have a problem exporting a model with a Morpher modifier if the normals cache is not being displayed properly.
Do not use bitmap filetypes that Max doesn't know how to read.
Using unknown bitmap types on world geometry and displacements will crash the VMF Exporter. This currently happens if using VTFs in materials in 3ds Max 2013 since there is no VTF plugin yet.
Understanding Displacement Blend Texture Scale
This page explains one cause for displacement materials to be scaled incorrectly in Source as well as the solution. You should use bitmaps of equal dimensions in both materials controlling the Blend material.
The Wall Worm Material Library Generator originally created DirectX Materials for all materials. But updates to the VMF Exporter changed the way materials are interpretted. Whenever possible, you should not use DirectX Materials.