Repairing of web server configuration for example.com fails: Error: Lock violation

Symptoms

The following error appear during the creation of a subscription backup:

PLESK_WARN: WARNING: (Subscription object ‘example.com’) Unable to back up configuration of error documents. Error: Failed to exec websrvmng: Exit code: 1: Filename : ?C:Inetpubvhostsexample.com.comhttpdocsweb.config Line number : 6 Error: Lock violation

Web.config of the affected domain redefines error status to custom error page:

<configuration>
    <system.webServer>
        <httpErrors>
            <remove statusCode="451" />
            <error statusCode="451" path="C:Program Files (x86)PleskAdditionalErrorDocs451.htm" />
        </httpErrors>
    </system.webServer>
</configuration>

Cause

<httpErrors> directive already defined by IIS and it conflicts with settings in domain’s web.config file

Resolution

Adjust web.config for the domain: 

1. Log into Plesk > Domains > example.com > File Manager 
2. Open web.config file, remove the following lines and save the file:

   <remove statusCode="451" />
   <error statusCode="451" path="C:Program Files (x86)PleskAdditionalErrorDocs451.htm" />