I am really sorry for the delay of this reply as it is actually a public day off for us here. I believe you are hitting this error because there is mod_security installed which prevents certain data from being posted to the server. It's best that you contact your hosting provider to look into this.
Whenever you hit "Forbidden Access" errors, they are 99% of the time being generated by your web server because the calls did not even reach Joomla's index.php file