Type 'System.Web.UI.UpdatePanel' does not have a public property named , asp.net, ajaxtoolkit

You get this error when you have a control inside a Update panel but not inside the ContentTemplate of the update panel.The right way to use the updatepanel is listed below

<asp:UpdatePanel ID="UpdatePanel1" runat="server>
     <ContentTemplate>
           < Your Control goes here >
    </ContentTemplate>
</asp:UpdatePanel>