ScriptManager has no IsNavigating property

I want to follow instructions from this video and add Back/Forward button support to a wizard (System.Web.UI.WebControls.Wizard). However, the ScriptManager object in my code has no IsNavigating property.

Why?

What do I have to install? (I have .NET Framework 3.5 SP1 insta开发者_开发技巧lled)

What version of System.Web.Extensions should I see in GAC? (I have 3.5.0.0)

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Did you select the framework as 3.5 when you created the project?

Edit: It seems your project was developed using .net framework 2.0. This is the reason why you had to convert the project to VS 2008.