Could not load type 'System.Web.UI.ScriptReferenceBase'

I am currently working on a web site project using AjaxControlToolKit with .NET3.5 SP1.
Today I deploy the web site into a test server Windows 2008.
I was surprised as I got this message on the browser:
Could not load type 'System.Web.UI.ScriptReferenceBase' from assembly 'System.Web.Extensions, Version=3.5.0.0,...

After workaround I found that .NET3.5 is installed on my machine but not on the server.
But with this tricky solution, I did not need to install .NET3.5 SP1 version on server nor recompile my web site with .NET 3.5.

Replace ajaxToolkit:ToolkitScriptManager to asp:ScriptManager in the aspx file.