I’m getting this error message when trying to run my application. I don’t know how to fix it:
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.
Here’s a screenshot of the error page:

What can I do to fix this error?
Use aspnet_regiis.exe to register version of .NET framework you are using.
This is a common issue and happens when IIS is installed after VS or .NET framework.
Note – for Windows 8/10 users, see the other answer by JohnOpincar below. And also the comment/tip from Kevin Brydon.