Need help with API tutorial on asp.net

Hello,

I'm working through the tutorial on http://www.asp.net/web-api/tutorials/hands-on-labs/build-restful-apis-with-aspnet-web-api 

I get to the place where it says to add the code:

public string[] Get() { return new string[] { "Hello", "World" }; }

So far so good. But it says that 'string' is not a correct variable, and as the next step is run (F5) it falls over saying " Could not load type 'ContactManager.WebApiApplication'."

OK, so what have i goofed?