Looks like a problem here because aspx files handler is not registered in IIS.
Here's what I did: installed Windows 8, then VS 2012 and at the end, .NET 3.5.
I create a new website and deploy my ASP.NET application. Application pool has both .NET Frameworks v2.0 and v4.0. I have selected one .NET Framework, let's say 4.0.
IIS tells me:
HTTP Error 404.3 - Not Found
The page you are requesting cannot be served because of the extension configuration. If the page is a script, add a handler. If the file should be downloaded, add a MIME map.
I am clueless, because what I understand from here is ASP.NET is not registered.
Also, on Windows 8 aspnet_regiis is not working and the trick of un-installing and then installing again .NET Framework by turn on/off feature from Control Panel does not solve anything.