In ASP.NET Application,I can't add a local webmethod to my project preferences

Question

First, I create a default Web Service(ASMX).And It has a default webMethod.just like:
public class WebService1 : System.Web.Services.WebService
{

    [WebMethod]  
    public string HelloWorld()  
    {  
        return "Hello World";  
    }  
}  

Next,I want to add this method to my objects's references, but it show some errors:

and the detail is

I don't konw why.
Please help me.

Answer 1

I finde the reason.
Because I webMethod in App_Code Files,So it can't be called.
if I move it to another place, it work success!