When I add any tool textures (skybox, trigger, clip, etc) to a brush and view it in the perspective view pane with 3D shaded textured Polygons (3D wireframe, filled polygons, and textured polygons work fine) and look at any tool texture, hammer instantly crashes.

Any ideas?

3D Shaded Textured is fucked, it happened with the last update. Use 3D Textured for now.

Solution here:
http://forums.thinking.withportals.com/hammer-exe-application-error-t684.html