Ajax Extension Works With Master Page But Not With Content Page

I have Installed Ajax Extension and added reference to the application. I am facing very strange problem that my master page accept the Ajax Extension Tools where as my content page throw error like “Element ScriptManager/UpdatePanel is not a known Element."

WebConfig:<?xml version="1.0"?><configuration><system.web><customErrors mode="Off"></customErrors><authentication mode="Windows"/><pages><controls><add tagPrefix="asp" namespace="System.Web.UI" assembly="System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/></controls></pages></system.web></configuration>


My contentPage:
<%@ Page Language="C#"  MasterPageFile="~/yuva.master" AutoEventWireup="true"   CodeBehind="PicSave.aspx.cs" Inherits="YuvaRK12.PicSave" %><asp:Content ID="MypicSave" runat="server"  ContentPlaceHolderID= "MainCPH" ><table id="Main" style="width:100%; height:350px; background-color:White;"><tr><td><asp:Label ID="lbl1" runat="server"></asp:Label><asp:Label ID="vis" runat="server" ></asp:Label><table id="Photo" style=" margin- margin-right:auto;"><tr><td><asp:FileUpload ID="FileUpload1" runat="server"  /></td></tr><tr><td><input  id="ImageBT"  
               type="button" 
               value="Upload Image" 
               runat="server" 
               onserverclick="ImageBT_ServerClick" style=" float:left;" /></td></tr><tr><td style="border-style:ridge;  border-width:3px;"><center><asp:Image id="MyImg" runat="server" 
                    style="width:150px; 
                    height:150px;"  
                    BorderStyle="solid" 
                    BorderWidth="1px"/></center></td></tr></table>  <!-- Photo End Here--><center><table><tr><td><asp:Button ID="SBtn" runat="server" 
                 Text="Submit" BorderStyle="ridge"  
                 BorderWidth="4px" 
                 OnClick="SBtn_Click" />

What I am missing here?. Very strange Ajax Extension is working with master page but not with content page!. What is the solution of it?.