I'm trying to add the Libspotify SDK to a test solution. However, I got the following error:

Now, I tried following the first answer of this question. However, all I got was:

The package of the library is structured in the following way:

Additionaly, my project is targeted to .NET Framework 4.0
And the configuration is done as follows:

What can I do to add this library?
EDIT:
Also, I found this link where someone explains that it need to be copied manually into the project output directory. I tried putting the .dll there, but I guess I have to modify something else to make it work. Any ideas?