This error is in all cases that CKEDITOR.getUrl() is called. Most notably the language file that CKEditor grabs first is from the wrong resource URL. In this case
Error can be like that :
GET http://localhost:3000/assets/admin/skins/moono/editor.css?t=EAPE ckeditor.js?body=1:78
GET http://localhost:3000/assets/admin/lang/en.js?t=EAPE ckeditor.js?body=1:78
Uncaught TypeError: Cannot set property ‘dir’ of undefined ckeditor.js?body=1:221
You can solve that using that javascript
<script>
window.CKEDITOR_BASEPATH="//localhost:3000/ckeditor/4.0.1.1/ckeditor/"
</script>