Symptoms
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Unable to access Plesk GUI, the following error is shown:
HTTP Error 503. The service is unavailable.
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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:
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Plesk Default application pool crashes several seconds after it has been restarted and the following error is shown in Event viewer:
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
Description:
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.
Cause
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.
Resolution
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Connect to the server via RDP
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Go to IIS > Sites > PleskControlPanel > ISAPI Filters > Remove third-party ISAPI filters, keep only the Plesk rewrite filter as shown in the following screenshot: