use ajax, json object to call webservice in asp.net using VB and getting error method error 500 .Any help will be appreciated

HERE IS MY WEBSERCIE.ASMX.VB 
Imports System.Web Imports System.Web.Services Imports System.Web.Services.Protocols Imports System.Configuration Imports System.Data Imports System.Data.SqlClient Imports AjaxControlToolkit Imports System.Collections.Specialized Imports System.ComponentModel
' To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line. <System.Web.Script.Services.ScriptService()> _ <System.Web.Services.WebService(Namespace:="http://tempuri.org/")> _ <System.Web.Services.WebServiceBinding(ConformsTo:=WsiProfiles.BasicProfile1_1)> _ <Global.Microsoft.VisualBasic.CompilerServices.DesignerGenerated()> _ Public Class WebService1 Inherits System.Web.Services.WebService
Dim con As New ADODB.Connection Dim conStr As String = System.Configuration.ConfigurationManager.ConnectionStrings("Connecti ...