Error message on site header

That is a common warning that we've seen before with JFBConnect and doesn't cause any functional problems. I wouldn't worry about it, unless you are having any problems with the site or extension functioning correctly. Your error reporting level in Joomla Global Configuration settings should be switched to something not as strict. It sounds like it is on Maximum or Development mode. Switching to Simple should remove the warning.

-Melissa

That error isn't caused by JFBConnect. We're trying to set a cookie at that line, but a cookie can only be sent if it's sent before any HTML is sent to the browser. In your case, the plg_nb_vm_wishlist/plg_nb_vm_wishlist.php plugin is sending some HTML first which is breaking the normal operation of cookies.

In general, Joomla will buffer all HTML before it's supposed to be sent and push it all to the user at once. If something is interrupting that flow and trying to send some HTML before the rest of the page it causes these types of warning messages, is inefficient and not the right way for Joomla plugins to operate.

I'd look into that plugin to understand why it's sending some output to the user way before it's supposed to.

I hope that helps,
Alex