Error: Sys.InvalidOperationException: Two components with the same id 'RadProgressBar1' can't be added to the application.
Workaround: Use RadScriptManager
<asp:ScriptManager ID="Scriptmanager1" runat="server" /> <-- issue
<%--<telerik:RadScriptManager runat="server" ID="rsm1"></telerik:RadScriptManager>--%> <-- workaround
<asp:UpdatePanel ID="Updatepanel1" runat="server">
<ContentTemplate>
<asp:Button ID="Button1" Text="AJAX" runat="server" />
<telerik:RadProgressBar runat="server" ID="RadProgressBar1" />
</ContentTemplate>
</asp:UpdatePanel>