AjaxControlToolkit requires ASP.NET Ajax 4.0 scripts

Try this:

Change

<asp:ScriptManager ID="scriptManager1" runat="server"></asp:ScriptManager> 

to

<ajaxToolkit:ToolkitScriptManager ID="toolkitScriptManager1" runat="server"></ajaxToolkit:ToolkitScriptManager> 

Check if this link helps you resolve your issue -

http://blog.thinkoriginally.com/2010/05/03/microsoft-jscript-runtime-error-ajaxcontroltoolkit-requires-asp-net-ajax-4-0-scripts/

EDIT: Check this link for dll load error resolution -

http://geekswithblogs.net/LessonsLearned/archive/2008/08/21/hidden-surprises-in-.net-3.5-service-pack-1.aspx


Try deleting Microsoft.ScriptManager.MSAjax.dll in the bin folder..