Twitter will always redirect to the login/register page if the user doesn't have an account. Twitter does not provide any way to get the user's email address, so we have to redirect to some registration flow (Joomla, JFBConnect, JomSocial, EasySocial are currently supported) to let the user fill out that, and any other, missing information.
As for the COM_JFBCONNECT_UNABLE_TO_RETRIEVE_USER message, that happens when JFBConnect can't fetch any information about the user that just registered. Google is very picky about the URLs that are used for communication. The URL you posted above looks like it's being modified by a 3rd party SEF extension. Can you try disabling that extension (temporarily) or having it 'skip' SEF URLs for JFBConnect altogether and try again? Once our URLs aren't being manipulated, my guess is that Google authentication should work better.
Thanks,
Alex