When System - JFBCSystem plugin is enabled I get this error ..

Iveth,
The error is stating that you are running out of RAM for Apache. It looks like your server is configured to use up to about 130MB per page load, which should be way more than enough. For reference, this site is configured to 80MB, but only use about 15MB per page on average).

When you enable the JFBCSystem plugin, it simply causing your site to go over the memory limit. The JFBCSystem plugin doesn't use a lot of memory, it's just simply the tipping point that's causing the problem. The error your seeing is actually being thrown in a core Joomla library.

To fix, you should either disable unused extensions on your site or increase the memory limit of your web server (how to do this is server specific and you'd need to contact your host).

Hope that helps,
Alex

Iveth,
Fixed. The issue is a strange one that is very uncommon. It basically happens if you install JFBConnect, never save any settings in the configuration area, and then enable the JomSocial plugin. To fix, I simply disabled the plugin, went to JFBConnect Configuration and hit "Apply" (not changing any settings), and then was able to successfully enable the JomSocial plugin.

Sorry for the inconvenience, you shouldn't run into it anymore.

Thanks,
Alex

No problem. Sorry for the troubles, but hopefully, it all goes smoothly from here.

Thanks,
Alex