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'

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

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

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