Article ID: 6735, created on Sep 30, 2009, last review on Oct 11, 2016

  • Applies to:
  • Plesk 12.5 for Windows
  • Plesk 11.0 for Windows
  • Plesk 11.5 for Windows


Upon trying to open Plesk in your browser you receive the following error:

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. Third-party ISAPI filters are registered in the PleskControlPanel website as shown in the following screenshot:

Plesk Default application pool crashes several seconds after restart with an error such as :

Log Name:      System
 Source:        Microsoft-Windows-WAS
 Date:          9/29/2009 1:02:52 PM
 Event ID:      5139
 Task Category: None
 Level:         Warning
 Keywords:      Classic
 User:          N/A
 Computer:      Test
 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 the third-party ISAPI filter configured for the PleskControlPanel website, which cannot run at the same time as the Plesk rewrite filter.


Remove third-party ISAPI filters from PleskControlPanel website configuration and keep only the Plesk rewrite filter as shown in the following screenshot:

See also

Where did my IIS7 server go? Troubleshooting 503 "service unavailable" errors by Mike Volodarsky

Search Words

Unable to login to control panel HTTP Error 503

Third-party ISAPI filters

Unable to login to control panel

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