Set focus inside an Update Panel

//***************************************************************************************

    //Code behind    protected void RadioButton1_CheckedChanged(object sender, EventArgs e)    {        SetMyFocus(ref TextBox1);        TextBox1.Focus();    }    private void SetMyFocus(ref TextBox txtBox)    {        string focusString = "setTimeout(/"$('" + txtBox.ClientID + "').focus(); /", 100);";        ClientScript.RegisterStartupScript(this.GetType(), "focusString", focusString, true);    }    protected void RadioButton2_CheckedChanged(object sender, EventArgs e)    {        SetMyFocus(ref TextBox2);        TextBox2.Focus();    }

 
//***************************************************************************************

 The following code is from the source view of the page

 
<%@ Page Language="C#" MasterPageFile="~/Test.master" AutoEventWireup="true" CodeFile="Test.aspx.cs" Inherits="Test" Title="Untitled Page" %><%@ Register Assembly="Microsoft.Web.Atlas" Namespace="Microsoft.Web.UI" TagPrefix="cc1" %><asp:Content ID="Content1" ContentPlaceHolderID="CPHTest" Runat="Server">       <cc1:ScriptManager ID="ScriptManager2" runat="server" EnablePartialRendering="true">   </cc1:ScriptManager>    <cc1:UpdatePanel ID="UpdatePanel1" runat="server">      <ContentTemplate>          <asp:RadioButton ID="RadioButton1" runat="server" AutoPostBack="True" OnCheckedChanged="RadioButton1_CheckedChanged" GroupName="Group1" /><br />          <asp:RadioButton ID="RadioButton2" runat="server" AutoPostBack="True" GroupName="Group1" OnCheckedChanged="RadioButton2_CheckedChanged" /><br />          <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox><br />          <asp:TextBox ID="TextBox2" runat="server"></asp:TextBox><br />          <asp:TextBox ID="TextBox3" runat="server"></asp:TextBox><br />                 </ContentTemplate>    </cc1:UpdatePanel></asp:Content>