title: Cannot call webmethod with jquery json
body: <p>I use the protocol jsonp to call web methods.</p>
  
  <p>I use this code for the webservice:</p>
  
  <pre><code>public class Service1 : System.Web.Services.WebService
  {
      [WebMethod]
      [ScriptMethod]
      public string HelloWorld()
      {
          return "Hello World";
      }
  }
  </code></pre>
  
  <p>And this on Jquery with jason on client side:</p>
  
  <pre><code>        $.ajax({
              type: "POST",
              contentType: "application/json; charset=utf-8",
              url: 'http://localhost:50837/Service1.asmx/HelloWorld',
              data: {},
              dataType: "json",
  
              success: function(Msg) {
                  alert('success:' + Msg.d.FirstName);
  
              },
              error: function(xhr, textStatus, errorThrown) {
                  alert("error");
              }
  
          });
  
      }
  </code></pre>
  
  <p>This Jquery gives me always an error message, but I don't know the reason. 
  Someone can help me?</p>