Jquery - JSON Can Call Method In .aspx File But Not In .asmx (web Service) File

I am using JQuery & JSON (POST) to call webmethod. However I can call only webmethod located at aspx file but not in asmx file Below are sample codes

CustomValidate.asmx
Imports System.Web.Services
Imports System.Web.Services.Protocols
Imports System.ComponentModel
Public Class CustomValidate
Inherits System.Web.Services.WebService
'ACCESS VIA JSON
<System.Web.Services.WebMethod()> _
Public Shared Function AJAX_Test(ByVal date1) As Boolean...
Return True
End Function
End Class
Javascript: JQuery JSON
function isDates(source, arguments) {
var isValidDate;
$.ajax({
type: "POST",
contentType: "application/json; charset=utf-8",
url: "CustomValidate.asmx/AJAX_Test",
data: '{date1: "' + arguments.Value + '"}',
dataType: "json",
async: false,
success: function(result) {
isValidDate = result;
},
error: function(httpRequest, textStatus, errorThrown) {
alert("status=" + textStatus + ",error=" + errorThrown);
}
});
arguments.IsValid = isValidDate;
}

It always return javascript undefined error. But if I put the AJAX_Test webmethod in aspx page and replace the url: "CustomValidate.asmx/AJAX_Test" to "mypage.aspx/AJAX_Test". It works fine.