We are using JFBConnect for a while now and the redirect works fine on most pages.
Only at Free Style Support at create a new ticket when a user logs in with facebook it redirects to a 500 error page.
Hope you can help us out.
How do you have the redirect setup in JFBConnect: A specific menu item or 'same page'? On the 500 error page, can you tell me what the actual error message is?
Beyond that, I'd check if there are any plugins or other features that may also be trying to perform a redirect when the user authenticates on that page to see if there's some sort of conflict happening.