Domain or Plesk shows Error 500.19: Cannot add duplicate collection entry of type 'mimeMap' with unique key attribute 'fileExtension'

Symptoms

Domain or Plesk shows the following error:

CONFIG_TEXT: Error 500.19: Cannot add duplicate collection entry of type 'mimeMap' with unique key attribute 'fileExtension' set to '.srt'

In other case only website's static content like images, .css, .js files cannot be loaded.

Error like the one above can occur while accessing Domains > example.com > IIS Settings

Cause

Two identical MIME types are specified for the domain and in server-wide IIS settings.

Resolution

Remove the MIME type specified in the error from the domain's settings or server-wide:

Server level:

1. Log in to the server via RDP
2. Go to IIS > Server > MIME Types and remove affected MIME type

Domain level:

1. Log in Plesk
2. Browse to Domains > example.com > IIS Settings and remove MIME type from the error

Note: If Plesk is inaccessible with the error, the website in IIS that has to be fixed is pleskcontolpanel

Another solution is to remove duplicated records from C:\Inetpub\vhosts\example.com\httpdocs\web.config