AjaxControlToolkit.ToolkitScriptManager is not available in version 16.1.1.0

This is intended. ToolkitScriptManager was removed in v15.1. Please follow the upgrade guide to resolve this issue.

What worked for me was changing this:

<ajaxToolKit:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server">
</ajaxToolKit:ToolkitScriptManager>

To this:

<asp:ScriptManager ID="ToolkitScriptManager1" runat="server">
</asp:ScriptManager>

My original tagPrefix is ajaxToolKit whereas OP prefix is cc1, but same concept.

Everything in my project worked like a charm after this.

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