AJAX Control Toolkit Assembly loading error

I encounter a problem...error is ....Ajaxcontroltoolkit.dll is in bin folder, but still I get this follwoing error...

Could not load file or assembly 'AjaxControlToolki开发者_开发百科t' or one of its dependencies. The module was expected to contain an assembly manifest.

My code is (in .aspx file):

<%@ Register Assembly="AjaxControlToolkit" TagPrefix="act"
    Namespace="AjaxControlToolkit" %>

What should I do?

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Do you have ASP.NET AJAX Extensions installed on your machine?