I have create a text box autofill using .asmx file its worling fine
here the code
But after this when i insert , separator this will repeat all the
previous values that is already filled in textbox please guide me or
send me how to do this

<form id="form1" runat="server">
        <asp:ScriptManager ID="ScriptManager1" runat="server"
EnablePageMethods="true">
            <Services>
                <asp:ServiceReference Path="~/autocomplete.asmx" />
            </Services>
        </asp:ScriptManager>
        <asp:TextBox ID="TextBox1" runat="server" Width="266px"></
asp:TextBox><div>
            <cc1:AutoCompleteExtender ID="AutoCompleteExtender1"
runat="server"
            TargetControlID="TextBox1"
            MinimumPrefixLength="1"
            ScriptPath="~/autocomplete.asmx"
            ServiceMethod="ListUser" ServicePath="">
            </cc1:AutoCompleteExtender>
        </div>
    </form>
//---------------------
[WebMethod]
    public string[] ListUser(string prefixText)
    {
     //return all records whose Title starts with the prefix input
string

        //int count = 10;
        string sql = "select BhootName from bhoot where bhootname like
@prefixText";
        SqlDataAdapter da = new SqlDataAdapter(sql, "Data
Source=vivacity5\\SQLEXPRESS;Initial Catalog=practice;Integrated
Security=True");
        da.SelectCommand.Parameters.Add("@prefixText",
SqlDbType.VarChar, 50).Value = prefixText + "%";
        DataTable dt = new DataTable();
        da.Fill(dt);
        string[] items = new string[dt.Rows.Count];
        int i = 0;
        foreach (DataRow dr in dt.Rows)
        {
            items.SetValue(dr["BhootName"].ToString(), i);
            i++;
        }
        return items;
    }

Regards,
Anil