If you're deploying a WCF Web API application to your IIS 7.x you might receive a HTTP Error 404.0 (MapRequestHandler / StaticFile):
As you know, WCF Web API relies on .NET Framework 4.0.
So lets take a look into the application pool for our application:
Everything looks fine here.
So lets dig a little bit deeper -- namely inspect the ISAPI Filters:
Looks like ASP.NET 4 is missing here... so lets fix it:
PS C:\Windows\Microsoft.NET\Framework64\v4.0.30319> .\aspnet_regiis.exe -i
Start installing ASP.NET (4.0.30319).
Finished installing ASP.NET (4.0.30319).
Now hit F5 in your browser:
(If it's not working after installing ASP.NET 4.0.x please review the version in your application pools settings again and fix it if necessary).