Someone who imported a model would be quite surprised if exporting the same model silently overwrote the oliginal file. So I make people choose the output folder manually.

Please try with the latest version available on http://blender.org.

Please upload your blend file.

http://www.pasteall.org/blend/

Mesh.calc_normals_split(): takes at most 0 arguments, got 1

This is very odd. Are you using an official release of Blender?

I'm not sure from your post whether the animation imported successfully? If it has, you can use the Source Engine Exportables to quickly change an Armature's current Action.

I'm trying to fix your NoneType error, can you upload the file again please?

Looks like the bad studiomdl behaviour is because you don't have $concave in your QC.

https://developer.valvesoftware.com/wiki/$collisionmodel

I can't reproduce this. Please send me the file in its broken state.

Install the Left 4 Dead 2 Authoring Tools from the Tools section of your library.

Upgrade Blender.