If you get an blank page when you try connect to ETS Inside server, then please open the URL 'http://YourServer'sAddress:8081/js/lib/cldr-data/supplemental/plurals.json' in your browser. If there is a problem with the mime-type mapping, then the browser should display the following 404.3 IIS error page:
If this page is not displayed, but the Developer Tools (by pressing F12 in your browser) indicate Status Code 404, this could be due to the IIS have being configured not to show the error pages, but the cause is the same (missing 'MIME-Type' mapping).
How to solve?
Open the IIS-Manager and open the 'MIME-Type' feature
Verify that the mapping is indeed missing. If so, click 'Insert…' to add a mapping. Fill out the modal dialog like this:
Afterwards the .json mapping should appear in the mime-type list.
Now, restart your ETS Inside server and try again to connect.