It seems you don't have the IIS7's ASP.NET feature installed.
First make sure you remove the .aspx extension from the MIME types, this is a security hole, and will cause the source code of your aspx to be downloaded.
Then go to appwiz.cpl -> Turn windows features on or off -> Internet Information Services -> World Wide Web Services -> Application Development Features -> ASP.NET
Once you have it installed you should be able to serve ASPX pages.
Thanks,
Mukhtar Desai
IIS Performance Team