Thank you for contacting us.
Please check if the following lines exist in the web.config
| <sitefinityConfiguration defaultProvider="XmlConfigProvider">
| <add name="XmlConfigProvider" type="Telerik.Sitefinity.Configuration.XmlConfigProvider, Telerik.Framework" />
If they do not exist add them to the <framework
section and the problem should be fixed.
Note: When upgrading Sitefinity you must also merge the changes in the web.config, because the new features may not work properly if their configuration is missing.
I hope this information will help you.
the Telerik team