the site for the url exists on both the local iis web server and the iis express web server

What is Applicationhost file

Application host file is mantaing the details of all application registerd in IIS.

What is machine.config file

The machine.config file contains default and the machine-specific value for all supported settings. The machine settings are controlled by the system administrator and applications are generally not given access to this file.

Machine.config file path

32-bit

x:\Windows\Microsoft.NET\Framework\[version]\config\machine.config

64-bit

x:\Windows\Microsoft.NET\Framework64\[version]\config\machine.config