My Rad version is Q1 2008 , when I use RadDatePicker , there's always a error that : "onclick is not valid attribute of element DateInput" , even I copy code example , it still have a same problem ... Can somebody help me resolve this. Thanks ! 
My aspx code is below
    
                                My aspx code is below
| <%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %> | 
| <%@ Register Assembly="Telerik.Web.UI" Namespace="Telerik.Web.UI" TagPrefix="telerik" %> | 
| <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> | 
| <html xmlns="http://www.w3.org/1999/xhtml" > | 
| <head runat="server"> | 
| <title>Untitled Page</title> | 
| </head> | 
| <body> | 
| <form id="form1" runat="server"> | 
| <telerik:RadScriptManager ID="RadScriptManager1" runat="server"> | 
| </telerik:RadScriptManager> | 
| <script type="text/javascript"> | 
| function ToggleFirstPopup() | 
| { | 
| $find("<%= RadDatePicker1.ClientID %>").showPopup(); | 
| } | 
| </script> | 
| <div> | 
| <telerik:RadDatePicker ID="RadDatePicker1" runat="server" Culture="English (United States)" | 
| SelectedDate="2008-11-19" Style="position: relative"> | 
| <DatePopupButton Visible = "true" > </DatePopupButton> | 
| <DateInput onclick = "ToggleFirstPopup()" DateFormat = "D"> | 
| </DateInput> | 
| </telerik:RadDatePicker> | 
| </div> | 
| </form> | 
| </body> | 
| </html> |