ajax AutoCompleteExtender 文本框没有反应；

后台代码。using System;
using System.Web;
using System.Collections;
using System.Web.Services;
using System.Web.Services.Protocols;
using System.IO;
using System.Net;
using System.Net.Sockets;
using System.Xml;
using System.Web.Script.Services;
using System.Data.SqlClient;
using System.Data;
using System.Data.Sql;
using System.Collections.Generic;/// <summary>
/// WebService 的摘要说明
/// </summary>
[WebService(Namespace = "http://tempuri.org/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
//[ScriptService]
[System.Web.Script.Services.ScriptService]
public class WebService : System.Web.Services.WebService {
    
    public WebService () {        //如果使用设计的组件，请取消注释以下行 
        //InitializeComponent(); 
    }    [WebMethod]
   
    public string[] FindDish(string prefixText,int count)
    {
        string strSql = "select DishName From Dish where DishName like '%"+prefixText+"%'";
        string strConn="Data Source=LIBAOZHEN\\LIBAOZHENSQL;Initial Catalog=GrogshopWeb;User ID=liuliu;Password=liuliu7765";
        SqlConnection conn=new SqlConnection(strConn);
        conn.Open();
        DataSet ds=new DataSet();
        SqlDataAdapter da=new SqlDataAdapter(strSql,conn);
        da.Fill(ds,"ds");
        DataTable dt=ds.Tables[0];
        string[] result=new string[dt.Rows.Count];
        for(int i=0;i<dt.Rows.Count;i++)
        {
            result.SetValue(dt.Rows[i][0],i);
        }
        conn.Close();
       
   
    }}页面代码      
<asp:ScriptManager ID="ScriptManager1" runat="server">
        <Services >
        <asp:ServiceReference  Path="~/WebService.asmx"/>
        </Services>
        </asp:ScriptManager>
        
        <br />
        搜索框：<asp:TextBox ID="Key" runat="server" >
        </asp:TextBox><asp:Button ID="Button1" runat="server"
            Text="查询" />
            
        <cc1:AutoCompleteExtender 
        ID="AutoCompleteExtender1" 
        runat="server" 
        TargetControlID="Key" 
        ServiceMethod="FindDish" 
        CompletionSetCount="3"
        ServicePath="WebService.asmx" 
        MinimumPrefixLength="1"
         CompletionInterval="1000" 
          Enabled="true"
       
        
        >
       
        </cc1:AutoCompleteExtender>