IIS 7 and Above
Configuration & Scripting
System.Web in Applicationhost.config not working anymore (IIS8.5)
Re: System.Web in Applicationhost.config not working anymore (IIS8.5)
Dec 03, 2014 10:31 PM|Pengzhen Song - MSFT|LINK
It seems that we can't configure it in applicationhost.config. As a workaround, you can try configuring it in machine root web.config file which locates C:\Windows\Microsoft.NET\Framework64\v4.0.30319\Config\web.config.(64bit machine)
Or only configuring for special site, we can set it in site root web.config files.