I'm having same issue. Logging in via JFBConnect with existing user account works fine, but when trying to register a new account using JFBConnect, the page goes into a continuous loop, clearing the registration page every few seconds.
When you close the browser and return to the site, it's still in the loop. The only way to break the loop is clearing browser cache.
This loop only seems to occur when using "Normal Registration". "Automatic Registration" seamlessly logs user in and avoids the continuous loop.
Site URL :
www.modusvia.com/development/misys/
See attachment for current JFBConnect config
Clean install with following config:
Joomla 2.5.6
JFBConnect 4.2.3
Tested in FF (13.0.1) and IE 9
Any help very much appreciated!