Plesk migration fails or website not accessible: There is a duplicate section defined

Symptoms

• Plesk Migration fails with error:

  example.com
  stdout: Filename: ?D:Inetpubvhostsexample.comhttpdocsweb.config
  Line number: 10
  Error: There is a duplicate 'example' section defined

• Cannot create domain backup in Plesk:

  Unable to back up configuration of error documents.
  Error: Failed to exec websrvmng:
  Exit code: 1: Filename: ?C:Inetpubvhostsexample.comweb.config
  Line number: 6 Error: There is a duplicate 'system.web.extensions/scripting/scriptResourceHandler' section defined

• An attempt to run plesk repair web example.com fails and website becomes not accessible:

  HTTP Error 500.19 - external Server Error
  ...
  Config Error: There is a duplicate 'system.web.extensions/scripting/scriptResourceHandler' section defined
  Config File: ?D:Inetpubvhostsexample.comcustom_dirtestdatabaseweb.config
  Config Source:
  13: <sectionGroup name="scripting" type="System.Web.Configuration.ScriptingSectionGroup, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=*********">

Cause

There is a duplicate section in the web.config file and in the upper-level configuration file.

Resolution

1. Log in to source Plesk panel

2. Go to Domains > example.com > File Manager

3. Open the file mentioned in the error message using a text editor and comment out the duplicate line of the mentioned number by
   <!-- at the beginning
   and --> at the end of the line.
   For example:

   <!-- <sectionGroup name="scripting" type="System.Web.Configuration.ScriptingSectionGroup, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=*********"> -->