A friend of me has a big problem: He's working on a Portal 2 map. It's just a test, but he has spent a lot of time in it, so he doesn't want to lose it.

Now, the map doesn't render anymore. The error, that shows up, is: "Load Portals: Couldn't find (file dir)/(file name).prt"

When I try to render the same .vmf file, it works, but my friend always gets this error.

So, where could be the problem?

I attached the .vmf file, so you can look at it yourself and perhaps try out if it will render in your editor.

Thanks in advance for your help!

There was an update not too long ago today. I'm not sure if that's relevant. Since you (Chikorita) can render/compile the map, I would think that your friend should try checking the integrity of the game files for both Portal 2 and the Authoring Tools to see if that helps.