Unknown server tag ‘asp:ScriptManager’ After having AjaxControlToolkit.dll referenced

Yesterday I was working on a project which had the AJAX Extensions in use. It’s primarily a .NET 2.0 application and I had .NET Framework 3.5 SP 1 installed on my system. It was working normally and all of a sudden I got this error that: Unknown server tag ‘asp:ScriptManager’

It was strange because every thing was working and I had the reference to the AjaxControlToolkit.dll.

I found out that by adding the section below to the <system.web> node in the web.config solves the problem:-


<add tagPrefix=”asp” namespace=”System.Web.UI” assembly=”System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35″ />




Author: Imran Akram

A .NET/SharePoint Consultant and a political enthusiast who believes in putting the feet of the elected and/or unelected officials to fire in order to get good governance.

10 thoughts on “Unknown server tag ‘asp:ScriptManager’ After having AjaxControlToolkit.dll referenced”

  1. I do what you say but another error appeared , the error is :
    Could not load file or assembly ‘System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35’ or one of its dependencies. The system cannot find the file specified.

    Source Error:

    [No relevant source lines]

    1. That’s weird. I think its just because you’re missing the reference to AjaxControlToolkit.dll. If not try adding it to the GAC.

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