There was a problem creating or writing to the fteditor.conf file. This file needs to be automatically generated by this application, or manually added by you into the same directory as fteditor.php
Most likely this error can be fixed by giving your web server user (www-data) permission to the current directory.
file_put_contents(/var/www/html/fantasticeditor/editor/1.4/fteditor.conf): Failed to open stream: Permission denied