The error I get is:
The virtual path 'null' maps to another application, which is not allowed.
I created an MVC 3 project and posted it as-is. Turn off the "URL Rewrite" and everything works fine. Turn it back on and you get the error.
The key to making this work is have MVC on port 80 and have the inbound websites on a different port, so the Controller can rewrite them to port 80. I sent port 80 web traffic on my Cisco to get to the web farm on port 591, then had the controller rewrite it to port 80 on the web farm. Why? This allows you to have a web server on the Controller as well. Ultimately probably a bad idea. LOL.