Recently one of my clients applicationHost.config files became corrupted, it might my fault because I was editing that file with notepad, and something went wrong.

Anyways IIS7 was erroring out with the error below when I tried to access the websites and application pools. So all websites and web applications were unavailable.

The Windows Process Activation Service encountered an error trying to read configuration data from file ‘\\?\C:\Windows\system32\inetsrv\config\applicationHost.config’, line number ’1′. The error message is: ‘Configuration file is not well-formed XML’

The applicationHost.config is situated on C:\Windows\system32\inetsrv\config\applicationHost.config

To access the history of the applicationHost.config file.

1. Browse to C:\inetpub\history directory
2. Inside this directory you will find a list of folders with the history of all the applicationHost.config file.
3. Pick a applicationHost.config file that you know is not corrupted. I usually pick one a few hours back to be safe.
4. Copy the applicationHost.config file and paste it into the C:\Windows\system32\inetsrv\config directory, replacing the corrupted file.
5. Now attempt to access IIS7 again. This time IIS7 should open, and you should be able to access all your sites and web apps.