Service Unavailable error message on a server with Plesk Windows
Plesk Error : Service Unavailable
Error under Event Viewer :
The identity of application pool ‘PleskControlPanel’ is invalid, so the World Wide Web Publishing Service can not create a worker process to serve the application pool. Therefore, the application pool has been disabled.
Try Plesk Reconfigurator > Repair Plesk Installation with checked option Plesk Services this fixed the issue which I faced.