Maria,
I don't have the admin credentials you sent anymore. I clear those out of my PM's frequently as I don't like having a lot of credentials to user's sites in my inbox. It seems insecure, though there shouldn't be any problem with it.
As for your issue with the JFBCSystem plugin, can you please go to Joomla Global Configuration and disable GZip compression and set Error Reporting to "Maximum". Also, disable any other 'optimization' plugins you may have enabled.
Then, enable the JFBCSystem plugin again and let us know what error is appearing on the site. That will help us diagnose the problem. Also, please let us know:
* Does the error shows up on every front-end page, or just specific ones.
* Does it only happen on the front-end, or the admin area too?
You can re-send the admin credentials as well, and we can take a look later today or tomorrow as well, but if you can tell us the error you're seeing, that will speed things up.
Thanks,
Alex