Could you please confirm that you are logged as Administrator?
The first time you activate a RadEditor feature, you must be logged as an
Administrator user. This is required, because the editor needs to update the
default list editing template by copying a file - from \TEMPLATE\FEATURES\RadEditorFeature\RadEditorList.ascx to
The file is copied by the IIS worker process, which in turn is impersonating
the currently logged in user.
All the best,
the Telerik team