Hi, 

try this :

Editor1.SetSecurity("Gallery,Image", "*", "FileProviderType", typeof(SqlFileProvider).AssemblyQualifiedName);

the first parameter specified the categories which you want to apply the security setting .

"*" means all , "Gallery" means insertgallery dialog with thumbnails , "Image" means  the simple file dialog for images

The predefined categories are 

Gallery,Image,Video,Document,Template 

check this about the configuration : http://richtexteditor.com/document/scr/html/image-gallery-path.htm 

Regards,

Terry