You may get following HTTP error if you don’t have ASP feature installed in IIS 7/7.5/8/8.5 server.

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.

HTTP Error 404.3

Causes

  • It’s possible a handler mapping is absent. By default, the static file handler functions all content.
  • The feature you want to use might not be installed.
  • The correct MIME map is not allowed for the application or website. (Cautionary: Do not make a MIME map for content that users shouldn’t download like .config files or .aspx pages)
  • If ASP.NET doesn’t installed.

How to fix HTTP Error 404.3 – Not Found

You need to install IIS sub components from

Control Panel -> Programs and Features -> Turn Windows features on or off

Programs and Features

Windows features

Internet Information Services -> World Wide Web Services -> Application Development Features

Application Development Features

After that, you should check ASP.NET option. After clicking on ASP.NET option ISAPI Filters, ISAPI Extensions, .NET Extensibility options will be selected automatically. Make sure that specific version is checked. These options are divided into 4 and 4.6 in Windows server.

IIS Options

Run the following command from cmd:

For 32bit (x86) Windows:

%windir%\Microsoft.NET\Framework\v4.0.30319\aspnet_regiis.exe -ir

For 64bit (x64) Windows

%windir%\Microsoft.NET\Framework64\v4.0.30319\aspnet_regiis.exe -ir
Note: .NET framework version can be changed. So make sure which framework version is in the %windir%\Microsoft.NET\Framework64 directory and run the command accordingly before running.

Lastly, check in IIS manager, that your application uses application pool with .NET framework version 4.0.