title: .NET Framework 3.5 and System.Net.Http not found
body: <p>I have a framework 3.5 project containing some asmx files. 
  When I have exception in asmx methods, I want return an error response:</p>
  
  <pre><code>try{
  ...
  ...
  catch (Exception ex)
  {
      var errorResponse = new HttpResponseMessage(HttpStatusCode.BadRequest)
      {
          Content = new StringContent(ex.Message), ReasonPhrase = ex.Message
      };
      return errorResponse;
  }
  </code></pre>
  
  <p>But I can't use HttpResponseMessage class because I can't reference Sytem.Net.Http namespace!</p>
  
  <p>Can anyone help me?
  Thx</p>