RadControls for ASP.NET AJAX
To add RadControls for ASP.NET AJAX to an existing ASP.NET web application you need to follow these steps:
Make sure you have installed ASP.NET AJAX. Info can be found at http://www.asp.net/AJAX/Documentation/Live/InstallingASPNETAJAX.aspx
If your web application is not using ASP.NET AJAX you need to configure it to do so. Detailed instructions can be found at http://www.asp.net/AJAX/Documentation/Live/ConfiguringASPNETAJAX.aspx (check the topic called Adding ASP.NET AJAX Configuration Elements to an Existing Web Site)
Add a ScriptManager control on top of the page in which you are going to add any RadControl.
<asp:ScriptManager ID="ScriptManager1" runat="server" />
If your page is a content page/user control you can add the ScriptManager control in your master/main page. For further details about the ScriptManager control you can check http://www.asp.net/AJAX/Documentation/Live/overview/ScriptManagerOverview.aspx.
4. Drag and drop a control from the RadControls for ASP.NET AJAX package.
The AJAX controls should be placed on the page after ScriptManager's declaration.