Failed to load plugin: plgauthenticationjfbconnectauth

I've never heard of that error before. It sounds like your authentication plugin folder has an issue (either a corrupt file or permissions issue).

When did this error start occuring? Did you change something with JFBConnect (or just install it for the first time)? Was there anything else that you changed recently?

From a very quick Google search, there are some recommendations to restore that directory from a backup, if possible. That may cause other issues if your backup doesn't have all the plugins that you've installed (since your database will still think they're there).

Let us know what happened, and we'll help how we can. I don't think this is a JFBConnect related issue though.

Thanks,
Alex

Glad you found the cause of the original issue. If you're getting that message when a real log message is trying to be created, it likely means that:
a) The directory you've specified for the log path is incorrect
b) The permissions on that directory (or the file trying to be written to) are incorrect. You'll need to make sure you have write permissions.

I hope that helps,
Alex