Not possible to change handler in Plesk: Cannot add duplicate collection entry of type with unique key attribute set to ...

Symptoms

Changing the handler (ASP status, PHP version, etc.) in the domain settings Home > Domains > example.com fails with the following error message:

PLESK_ERROR: Error: Cannot add duplicate collection entry of type 'add' with unique key attribute 'name' set to 'ASPClassic'

OR

Unable to access IIS settings for domain in Home > Domains > example.com. It's getting failed with the error message below:

PLESK_ERROR: Internal error: Filename: \\?\C:\Windows\system32\inetsrv\config\applicationHost.config
Line number: 182673 Error: Cannot add duplicate collection entry of type 'mimeMap' with unique key attribute 'fileExtension' set to '.woff'
In module Exception type:System.Runtime.InteropServices.COMException at Microsoft.Web.Administration.Interop.AppHostWritableAdminManager.GetAdminSection(String bstrSectionName, String bstrSectionPath) at
...
at execute "C:\Program Files (x86)\Parallels\Plesk\admin\bin64\websrvmng.exe" --get-mime-types "--vhost-name=example.com" "--vdir-name=/"(vconsoleapp::run line 117)
Error code 1)

Cause

IIS detects a duplicate entry for the same setting at a higher level in the configuration. Check the following Microsoft TechNet article for additional details

Resolution

1. Log in to the server via RDP

2. Open IIS Manager and remove the domain IIS > Sites > example.com

    

   Note: It will delete only IIS configuration of the website and left web content intact 

3. Re-create website configuration in IIS by runnig the following command in Command Prompt (cmd.exe):

   C:\> %plesk_dir%\bin\repair.exe --reconfigure-web-site -web-site-name example.com

If the steps above do not help, check domain's web.config file in %plesk_vhosts%\example.com\httpdocs folder and remove duplicate entry of the directive from the error message.

If the issue still persist, review IIS configuration file %windir%\system32\inetsrv\config\applicationHost.config and remove duplicate directives from the error for the domain as below:

1. Back up the current IIS configuration using the following command in cmd.exe :

   C:\> %windir%\system32\inetsrv\appcmd.exe add backup "My Backup Name"

2. Open the file %windir%\system32\inetsrv\config\applicationHost.config in a text editor and find the section containing the website configuration:

   <location path="example.com">
   

3. Under this section, find <handlers> and remove the string starting with the collection entry name shown in the error ( ASPClassic ):

   CONFIG_TEXT: <add name="ASPClassic" path="*.asp" verb="GET,HEAD,POST,TRACE" modules="IsapiModule" scriptProcessor="C:\Windows\System32\inetsrv\asp.dll" resourceType="Either" />

4. Save the changes made in the %windir%\system32\inetsrv\config\applicationHost.config file and try to perform the failed action again.

   Note: If the error occurs again with another attribute 'name' , delete it from the <handlers> section using the steps described above.