Your application pools may stop working and throw “HTTP 503 The service is unavailable” error with this description: “Trying to read configuration data from file ‘\\?\<EMPTY>’, line number ‘0’“. This issue generally happens after installing updates or making configuration changes in your server.
This error is displayed in Event Viewer with the event ID 2307:
The worker process for application pool X encountered an error ‘Cannot read configuration file due to insufficient permissions’ trying to read configuration data from file ‘\\?\EMPTY’, line number ‘0’. The data field contains the error code.
This issue occurs because of the problems happened while creating the virtual directory and application pool. Missing config files that might have been removed somehow could be another possible cause (possible suspect: Antivirus).
A few things to try to solve this issue:
Remove everything in the temp application pool directory (C:\inetpub\temp\apppools). This will require restarting the machine
Check antivirus software’s logs. It may be removing the config files in the temp\apppools folder. Define an exception for this folder if needed.
Check if IIS_IUSRS has Read access on application folders which are referenced by virtual folders
Make sure IIS_IUSRS has access for C:\inetpub\temp folder
Make sure that you have enough free disk space in the server
Execute chkdsk in Command Prompt and make sure fix the issues found