The Windows Process Activation Service encountered an error trying to read configuration data from file ‘\\?\C:\Windows\system32\inetsrv\config\applicationHost.config’, line number ’0′. The error message is: ‘Configuration file is not well-formed XML’
Uh oh! This has actually happened once to me before. IIS 7 was working great all day long, then at around 3 AM you get a page, you have a group of IIS7 servers with corrupted applicationHost.config files! Lucky for us there are backups made each time a change is made in IIS. Look under c:\inetpub\history\ and find the most recent one, see if it has a large enough file size, most of mine are over 5-10MB. Once you find it, copy it to c:\windows\system32\inetsrv\config\ and overwrite the existing files. Usually I would say backup what you have currently, but there really isn’t a point to doing that, what is there is corrupted.
Run an iisreset and make sure your server is up and running, if not you may have to go back a bit more until you find a working applicationHost.config file.+1 this post if it helped you!