I struggled with this long enough, and ended up guessing the right answer; maybe this will save someone else the trouble. On a Windows Server 2003 box, IIS 6, trying to get it to server .aspx pages from a virtual folder. I could get .html files to serve just fine, but trying to hit an .aspx file kept returning a 404 Not Found Error. I had to Open the 'Web Service Extensions' folder in IIS Manager, then 'Add a new Web service extension...' to add the .NET 4 application handling. I used the following:
- Extension Name: - "ASP.NET 4.0"