If you're getting 500 errors, there's a few things you can do to narrow the problem down:
* Set the "Error Reporting" setting in the Joomla Global Configuration area to "Maximum". Then, a PHP error message may show which can help narrow down the issue.
* Check the Apache server *and* PHP error logs to see what errors are reported there.
There's many things that can cause 500 errors. Disabling the JFBCSystem plugin obviously indicates our plugin is related, but we've seen many instances where it's a combination of more than one plugin that can cause 500 errors. It's possible that disabling other plugins may fix the issue as well. We'll need to narrow down the specific reason that there is an error to determine the proper solution.
Other things to try:
* Disable the Social Profiles - JomSocial plugin
* Disable the Open Graph - JomSocial plugin
See if the problem goes away when you do so and, if so, narrow down which plugin is the problem and we'll work from there.