Commented Issue: One more time: AjaxControlToolkit requires ASP.NET Ajax 4.0 scripts. [27340]

My ajaxcontroltoolkit was working fine until I selected "convert to web application" on the Solution Explorer. I now get the "Ajax 4.0 scripts" message with my project, and with both of my backups. I created a new project, same message. I uninstalled and reinstalled the toolkit, nothing. I even uninstalled and reinstalled Visual Studio Express 2012 for Web. No change. Here's my code from my master page. As I said, it's been working fine.

<ajaxToolkit:ToolkitScriptManager ID="ToolkitScriptManager1" EnablePageMethods="true" runat="server">

<Scripts>
<%--Framework scripts--%>
<asp:ScriptReference Name="jquery" />
<asp:ScriptReference Name="jquery.ui.combined" />
<asp:ScriptReference Name="WebForms.js" Path="~/Scripts/WebForms/WebForms.js" />
<asp:ScriptReference Name="WebUIValidation.js" Path="~/Scripts/WebForms/WebUIValidation.js" />
<asp:ScriptReference Name="MenuStandards.js" Path="~/Scripts/WebForms/MenuStandards.js" />
<asp:ScriptReference Name="GridView.js" Path="~/Scripts/WebForms/GridView.js" />
<asp:ScriptReference Name="DetailsView.js" Path="~/Scripts/WebForms/DetailsView.js" />
<asp:ScriptReference Name="TreeView.js" Path="~/Scripts/WebForms/TreeView.js" />
<asp:ScriptReference Name="WebParts.js" Path="~/Scripts/WebForms/WebParts.js" />
<asp:ScriptReference Name="Focus.js" Path="~/Scripts/WebForms/Focus.js" />
<asp:ScriptReference Name="WebFormsBundle" />
<%--Site scripts--%>
</Scripts>
</ajaxToolkit:ToolkitScriptManager>

tagprefix from web.config is

<add tagPrefix="ajaxToolkit" assembly="AjaxControlToolkit" namespace="AjaxControlToolkit" />

Comments: I've installed the January 2013 version of the toolkit, and changed the tagprefix to asp rather than ajaxtoolkit. Makes no difference. Same message.