ajax auto complete extender not working

<asp:TextBox ID="txtName" runat="server" Height="18px" Width="366px" 
            AutoPostBack="True" ></asp:TextBox>
        
<ajaxToolkit:AutoCompleteExtender
   runat="server" ID="autoComplete1"  TargetControlID="txtName"
ServicePath="WebService1.asmx" ServiceMethod="GetCompletionList"
 MinimumPrefixLength="1" />

[WebMethod, ScriptMethod]
        public static string[] GetCompletionList(string prefixText, int count)
        {
            if (count == 0)
        {
            count = 10;
        }
 
        if (prefixText.Equals("xyz"))
        {
            return new string[0];
        }
 
        Random random = new Random();
        List<string> items = new List<string>(count);
        for (int i = 0; i < count; i++)
        {
            char c1 = (char)random.Next(65, 90);
            char c2 = (char)random.Next(97, 122);
            char c3 = (char)random.Next(97, 122);
 
            items.Add(prefixText + c1 + c2 + c3);
        }
 
        return items.ToArray();
    
        }