We had no other plugins installed. Only Enfold theme on a WordPress 4.1. However we discovered the problem. We wanted to test the new centralized WordPress features in Plesk. And by enabling the security it messes up native WordPress scripts

http://cloud.righthere.com/image/420j0k0N421l

We disabled the security check on wp-includes and now the WordPress TinyMCE native editor works again.

Sorry for the trouble, but hope this can help others if they use the “security check” in Plesk for WordPress sites.