Could not find any resources appropriate for the specified culture or the neutral culture. Make sure "AjaxControlToolkit.Properties.Resources.NET4.resources" was correctly embedded or linked into assembly "AjaxControlToolkit" at compile time, or that all the satellite assemblies required are loadable and fully signed.

Thats the Error: 

Reason:  AjaxControlToolkit’s control load reference refers to the base System.Web.UI.Control method which is present as a part of the ASP.NET AJAX Libraries and those libraries are referenced only when the ScriptManager is referenced in the page.


Solution: - Add a ScriptManager control to your page.

<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>