If you tried {JLinkedLogin}, that's likely the issue. You should be using {JFBCLogin} for the "Login with Facebook" button. JLinked is our LinkedIn integration extension.
If that doesn't work, check the Social configuration area of JFBConnect and the "Misc" tag. There is an "Admin Render Key" setting there. Just leave it blank for now and hopefully that will help.
Finally, check if you have the System - Cache plugin enabled. If so, make sure it's the last (highest numbered) plugin. If you change these settings, also clean the Joomla Cache.
Hope that helps get you started, but if you need anything else, just let us know.
Thanks,
Alex