What about index.htm or index.html or default.php default.htm default.html and home.php etc etc
In IIS there is an order they are run in. So Check for all of them.
Also I have noticed that even when I am logged in as admin there are no "Edit" buttons next to each article at the top like there used to be.
It's like it doesn't know I am admin. Also it means I have to go into the back end, run a search to do any editing.
Why this has changed I don't know. I am thinking of a different plugin maybe http://wordpress.org/plugins/quick-cache/ which is recommended by s2member which is a framework for free membership and a good plugin if you need to sell subscriptions or payments on your site.
Worth a try.