title: CS0234: Missing Assembly Reference
body: <p>I have some missing assemblies in my PC, and don't have any idea how to fix it.</p>
  
  <p>When I create a new ASP.NET MVC 4 internet application from template (using VS 2012) everything works fine. As soon as I try to integrate Web API controller I get a missing assembly reference error. For example, when I create application using ASP.NET 4 Web API default template and click "API" on the interface I get Compilation error:</p>
  
  <pre><code>Compiler Error Message: CS0234: The type or namespace name 'Description' does not exist in the namespace 'System.Web.Http' (are you missing an assembly reference?)
  </code></pre>
  
  <p>I have checked the assembly and everything seems to be fine. It's in version 4.0. I have .NET framework 4.5  installed on my PC. Where should I look for the reason of the issue?</p>