You'll need to disable the JFBCSystem plugin. That should get your site back up and running, and then we can narrow down the actual issue.
If you have access to the admin area, please go to the Plugin Manager and disable the JFBCSystem plugin directly.
If you can't access the admin area, please edit the /plugins/system/jfbcsystem/jfbcsystem.php file. Around line 26, you'll see:
function __construct(& $subject, $config)
{Add 'return;' after that line, so it looks like:
function __construct(& $subject, $config)
{
return;
...don't touch anything else...
Once you can get back in your admin area, I'd recommend disabling the Open Graph - EasyBlog plugin as it sounds like that's where the error is coming from.
Then, you can remove the 'return;' line from the JFBCSystem plugin and JFBConnect should work like normal.
Hopefully that gets you going, but the EasyBlog integration with JFBConnect will be disabled. If you need that functioning, please let us know what the full error message is that you were getting so we can investigate. If you're no longer using EasyBlog, then you should be good to go.
I hope that helps,
Melissa
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