Please create a folder called Files
in the application root and this will fix the issue.
Actually setting the default path for the managers is quite complex, because so far we have not exposed proper configuration for this and this is something that we have added in our TODO list. You should map the template for CotentBlock
control which contains the declaration of HtmlField control that wraps RadEditor control. Note that HtmlField is required control. Then you can subscribe for OnPreRender and set the upload, delete paths
All the best
the Telerik team