Place ur script manager on the top of the pade under <asp:content xmlns:asp="#unknown">
<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ToolkitScriptManager>
and place all of the code in update panel which u do not want to load again and again
<asp:UpdatePanel ID="CustNameCodePnl" runat="server">
<ContentTemplate>
<%--Enter Your Code Here--%>