Some times ago I got this error using IIS:
HTTP Error 404.3-Not Found
The page you are requesting cannot be served because of the extension configuration. If the page is script, add a handler. If the file should be downloaded, add a MIME map.
I looked for a solution on Internet and I found this:
You should install IIS sub components from
Control Panel -> Programs and Features -> Turn Windows features on or off
Internet Information Services has subsection World Wide Web Services / Application Development Features
There you must check ASP.NET (.NET Extensibility, ISAPI Extensions, ISAPI Filters will be selected automatically). Double check that specific versions are checked. Under Windows Server 2012 R2, these options are split into 4 & 4.5.
Run from cmd:
Finally check in IIS manager, that your application uses application pool with .NET framework version v4.0.
Also, look at this answer.
This happen when you install Visual Studio before IIS; in this case you need only to run the command regiis