Default AJAX extension in VS 2010 does not work

I don't understand why my AJAX extension controls cannot be dragged into my code. When I drag one of the controls, nothing appear.

I tried to fix开发者_如何转开发 this problem by download the Ajax Control Toolkit, extract the AjaxControlToolkit.dll, create a new tab in ToolBox, select Choose Item, select AjaxControlToolkit.dll and press Ok. Then my new tab disappear. Or the tab remains, without any controls in it. However, when I check "Show All", the controls and disappeared tab does exist.

I need to use Ajax in asp.net. Really need help.

Ok I found the solution. My Windows 7 does not have .NET Framework 3.0 which is required by teh AJAX Control Toolkit. After install the .NET Framework in Control Panel->Program->"Turn Windows Features on or off" and changing the project to .NET Framework 3.5, it worked.