I have disabled auto activation but enabled recaptcha. Also the Jomsocial plugin is active, so the user is created into Jomsocial.
I enter all the details and the recaptcha correctly, however the registration thinks my recaptcha is always wrong and sends me to a different registration form with a different recaptcha. The error I get is:
The words you typed did not match the ones displayed. Please try again.
Edit: I want to point out that the first form is: component/jfbconnect/?view=loginregister while the second form is: option=com_users&view=registration
Are you using the built-in Joomla captcha?
I'm not sure why you're having that issue, but I'd honestly recommend disabling it from running on other forms than the standard Registration form from Joomla. By the time the user gets to the JFBConnect registration form, they've already authenticated through Facebook, so you should have high confidence that they aren't a bot. It's also one less hurdle for the Facebook people to have to deal with (another advantage of JFBConnect).
Hope that helps,