Resource not found 404 in MVC 3 at root level with IIS

Really annoying one this, IIS the other day was giving me the all too familiar 404 rescource not found at the root level when requesting my default path on an MVC 3 site.   If you haven't checked:

See if you can server any page from that address (any html page).  If this throws the same error, check the permissions settings for your site as I did this and it works.  Hope this helps somebody out there !