Preleminary of Ajax

1).Solution Exporer----------> Create Bin Folder----->Right Click the Bin folder----> Add Reference......> Browse----->Add  'AjaxControlToolkit'

2)In aspx design source file,
Add Register Directive as below
<%@ Register %>

3)Then within the <%@ Register %> add Tag Prefix, Assembly, NameSpace ....

4) <%@ Register TagPrefix="SRI" Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" %>

5) Assembly---> Simply Goto Solution Explorer---> Bin ----> AjaxControlToolkit.dll  then copy the AjaxControlToolkit and then give that name to  Assembly and Name space...

6) Add the Script Manager in aspx page

<asp:ScriptManager ID="ScriptManager1" runat="server">

    </asp:ScriptManager>

7) Add the UpdatePanel , then ContentTemplate and Within the contentTemplate  add the controls as below

<asp:UpdatePanel ID="UpdatePanel1" runat="server">

        <ContentTemplate>

            <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>

            <SRI:FilteredTextBoxExtender ID="TextBox1_FilteredTextBoxExtender"

                runat="server" Enabled="True" TargetControlID="TextBox1">

            </SRI:FilteredTextBoxExtender>

        </ContentTemplate>

    </asp:UpdatePanel>