Hello, I tried to update version 6.x to DNN 9.0.0. The installation page showed all "OK", but when I click on the "go to site", it shows

500 Internal Server Error
The requested Url does not return any valid content.

Administrators

Change this message by configuring a specific 404 Error Page or Url for this website.

log says:

2019-06-15 19:52:39,216 [Predator][Thread:68][ERROR] DotNetNuke.ComponentModel.ProviderInstaller - System.Configuration.ConfigurationErrorsException: Could not load provider DotNetNuke.HtmlEditor.FckHtmlEditorProvider.FckHtmlEditorProvider, DotNetNuke.FckHtmlEditorProvider

when i try to access localhost/Default.aspx, the site attempts to redirect to the "online version"

Same happens if I try to upgrade to DNN 8.0.0

Thank you for your help.

Libor