Change the way dnn is setup on your server - instead of hosting it in a subfolder of the wwwroot web application path - place it in its own separate application and hosting.  So somewhere like \inetpub\dnn\  - and create a website in iis that points directly to that folder.

Note however that once you do this you can no longer access dnn using 127.0.0.1 - instead you would then always access it using a domain name - dnn.localhost or some such which maps back to 127.0.0.1.

Also make sure you set the permissions up correctly on the new folder.

Westa