Unit Test for creating a sharepoint site fails

Question

I have some code that creates a sharepoint site.

When the code runs as part of the solution it works. However, when I run it as a unit test I get the following error:

The test adapter 'WebHostAdapter' threw an exception while running test 'CreateSiteTest'. The web site could not be configured correctly; getting ASP.NET process information failed. Requesting 'http://localhost/VSEnterpriseHelper.axd' returned an error: The remote server returned an error: (500) Internal Server Error. The remote server returned an error: (500) Internal Server Error.

I have the following tags on my test:

    [TestMethod()]
    [HostType("ASP.Net")]
    [UrlToTest("http://localhost/SitePages/Home.aspx")] 

Any Idea why I am getting this error?