How to use AjaxControlTookit's Tab Panel inside page inherited from masterpage

I'm trying to use both update panel and tab container on my page but when I compile the project I get this error...

The type 'System.Web.UI.ScriptControl' is defined in an assembly that is not referenced. You must add a reference to assembly 'System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35'.

I've already added the reference to the aspx page, web.config and still the 开发者_开发技巧build fails. Is there something else I need to do? What am I missing?

ps. Please let me know if you need me to provide any more information.

Thanks in advance.

you need to add that reference to your web.config.

<compilation debug="true">
  <assemblies>
    <add assembly="System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>