Unable to access Plesk GUI, the following error is shown:
HTTP Error 503. The service is unavailable.
Plesk uses IIS as a Web server. IIS Advanced Logging or IIS Mod-Rewrite is installed on the server. Going to IIS > Sites > PleskControlPanel > ISAPI Filters > There are third-party ISAPI filters registered as shown in the following screenshot:
Plesk Default application pool crashes several seconds after it has been restarted and the following error is shown in Event viewer:
Log Name: System
Date: 9/29/2009 1:02:52 PM
Event ID: 5139
Task Category: None
A listener channel for protocol 'http' in worker process '3768' serving application pool 'PleskControlPanel' reported a listener channel failure. The data field contains the error number.
This is caused by a third-party ISAPI filter configured for the PleskControlPanel website, which cannot run at the same time as the Plesk rewrite filter.
Connect to the server via RDP
Go to IIS > Sites > PleskControlPanel > ISAPI Filters > Remove third-party ISAPI filters, keep only the Plesk rewrite filter as shown in the following screenshot: