How to get VS ASP.NET unit testing to work?

Question

I'm trying to write a few test for an aspx page that handles posted xml.
The project runs fine on the visual studio's web development server (WebDev.WebServer40) but when I try to run a basic (empty) test like the one bellow, the test run results show me this error:

The host type 'ASP.NET' cannot be loaded for the following reason: The key 'ASP.NET' cannot be found.

I've tried all I could think of, but no go.

[TestMethod]
[HostType("ASP.NET")]
[AspNetDevelopmentServerHost("D:\\Documents\\Projects\\Web\\Osc.Framework\\", "/")]
[UrlToTest("http://localhost:24811/Default.aspx")]
public void Page_LoadTest()
{
    Assert.Inconclusive("A method that does not return a value cannot be verified.");
}

Any ideas on how to get this to work?