Can’t add links – error message

Thanks for your very nice plugin. I have one little problem. I can’t add links. When clicking the link button in the editor in drag n drop mode, nothing happens. Looking at the browser console, I can see some js errors:

load-scripts.php:9 JQMIGRATE: Migrate is installed, version 1.4.1
/wp-content/plugins/wp-ultimate-csv-importer/assets/js/ckeditor-js/contents.css?t=H0CG Failed to load resource: the server responded with a status of 404 (Not Found)
link.js Failed to load resource: the server responded with a status of 404 (Not Found)
ckeditor.js:622 Uncaught Error: [CKEDITOR.dialog.openDialog] Dialog "link" failed when loading definition.
    at a.openDialog (ckeditor.js:622)
    at a.<anonymous> (ckeditor.js:622)
    at f (ckeditor.js:244)
    at Array.B (ckeditor.js:244)
    at u (ckeditor.js:244)
    at HTMLScriptElement.CKEDITOR.env.ie.f.$.onerror (ckeditor.js:245)
contents.css Failed to load resource: the server responded with a status of 404 (Not Found)

Adding html link tags manually doesn’t work either in the visual editor. It will show the html code instead of parsing it.