In IIS 7.0 you should not use sf404 error page. Instead you should go to the Handler Mappings section of your website in IIS and create a new Wilcard Script Mapping. You should use the aspnet_isapi.dll as the executable to map to. Then you can go to the <cms> configuration section and set the pageExtension property to empy string (""
All the best,
the Telerik team
Registration for Q1 2011 What’s New Webinar Week is now open. Mark your calendar for the week starting March 21st and book your seat
for a walk through all the exciting stuff we ship with the new release!