I have a webmethod like this:
[WebMethod]
[ScriptMethod(UseHttpGet = true)]
public static string test(string Name, int? Age)
{
    return "returned value";
}
And the ajax call :
$.ajax({
  type: "GET",
  url: "form.aspx/test",
  data: {'Name': "n1", 'Age': 30},
  contentType: "application/json; charset=utf-8",
  success: function (data) {
    console.log(data);
  }
});
Without parameters/data it works, but when I try to pass some parameters I get this error: 
GET http://localhost:55410/test.aspx/test?Name=n1&Age=30
500 (Internal Server Error)
I think this's the detailed exception:
System.ArgumentException: Unknown web method form.
Parameter name: methodName
 
     
    