Instead of
<asp:scriptmanager id="ScriptManager1" runat="server" xmlns:asp="#unknown">
</asp:scriptmanager>
Try
<cc1:toolkitscriptmanager id="ScriptManager1" runat="server" xmlns:cc1="#unknown">
</cc1:toolkitscriptmanager>
And by the way, as you are using it inside a content page, it would be convinient to use the
ToolkitScriptManager
in the Master page.