QUOTE:

Also ensure that you are not using mixed domains for the Joomla! frontend and backend. For example if your site works with both www and non-www domain or http and https domain, ensure that the backend domain is exactly the same as the frontend one. Otherwise each javascript application running in the backend will be blocked by the browser itself because of cross domain policy returning a red bar 'Error' message. Take care if in the Joomla configuration.php you have hardcoded the domain in the $live_site variable, that variable must be left empty as by default.