Great! Glad I could help.

Feel free to mark the post as a solution so others can find it more easily if they run into the same issue as you.

This is a long shot but it might have something to do with your mirror modifier and the shape keys- since the addon tries to apply all modifiers before exporting, and the mirror modifier can't be used on a mesh with shape keys.

If you don't know where the video is from then I'm afraid that the addon I linked is the closest we are to being able to apply textures quicker.

There Is a way to import VTFs and VMTs in Blender with the help of a few surprisingly unheard of addon:
https://github.com/REDxEYE/io_texture_VTF

Where did you find that video? This is the first time I see such functionality, but if it exists, it can be done for Cycles, it just needs to link the textures differently so they work with Cycles.

It is otherwise theoretically possible to automatically import textures, like for example prompting the user to pick the game's root folder and then by parsing the QC and the model materials finding the proper textures, but that would be quite difficult to program and would be prone to issues. For now, feel free to try the addon above, it should make things a bit quicker than having to convert every single VTF before importing the texture into Blender.

You might want to try to create a new scene and import it to that, then link it to your work scene and delete the scene you just made. I'm pretty sure that error has something to do with importing armatures to a scene where an armature is already present, though that would be up to the developer to verify. You could also try the "create a new armature" option when importing, that might work and save you the hassle of making a new layer just to import something.

Does the layer you're importing it to have any other objects?

Try changing the armature option to when importing from append to create new one.

If you want, you can upload the files somewhere so we can take a look.

What does your QC file look like?

Try deleting everything in the scene before importing (including any hidden stuff if you have any).