You might have not registered the control in the page.
Or you had tagprefix as ajaxToolkit instead of cc1.
So verify it.
<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="cc1" %>
Or use ScriptManager instead of ToolkitScriptManager as it is removed in latest version.
<asp:ScriptManager ID="ScriptManager1" runat="server">