remove this line of code:---
Quote:
<asp:scriptmanager id="ScriptManager1" runat="server" xmlns:asp="#unknown">
Add this:-
Quote:
<asp:toolkitscriptmanager id="ToolkitScriptManager1" runat="server" xmlns:asp="#unknown">
Whenever u are using Extender controls u should use ToolkitScript manager insted of scriptmanager.