Chris,

I had a quite similar problem some days ago.

First thing is to use the DNNConnect.CKE provider as a default (chances are good that you are still using the Telerik RadEditor which is not supported anymore). Change the value of the default attribute of the htmlEditor to "DNNConnect.CKE" (in web.config). It should look like

<dotnetnuke>
   <htmlEditor defaultProvider="DNNConnect.CKE">
      <providers>
         <clear />
         <add name="DNNConnect.CKE" type="DNNConnect.CKEditorProvider.CKHtmlEditorProvider, DNNConnect.CKEditorProvider"
            providerPath="~/Providers/HtmlEditorProviders/DNNConnect.CKE/"
            settingsControlPath="~/Providers/HtmlEditorProviders/DNNConnect.CKE/Module/EditorConfigManager.ascx" />
      </providers>
   </htmlEditor>

If it does not work then you could try to make a clean install of DNN 9 somewhere and compare the web.configs. Most propably some things did not match correctly, so you have to do it manually. A good tool for that is WinMerge.

Happy DNNing!
Michael