Manish,
Thanks so much for letting us know how you got it going. I created a new Common Support Question with what you mentioned:
www.sourcecoast.com/jfbconnect/docs/comm...rt-questions#jfusion
If there are any other suggested settings you have, feel free to let us know.
For your solution, it definitely makes sense that that could make a difference. Basically, JFusion is setting a cookie telling PHPBB that a user is logged in. Using the other method that uses JFusion directly would likely send the unique username/password we send and have PHPBB do it's own authentication and create the cookie. That username/password wouldn't work for any user in PHPBB though, and so it would get denied.
We definitely appreciate the compliments for JFBConnect in general. It's taken many years to get it as solid as it is, and we're very happy that it 'just works' most of the time. Your situation was more complex, but glad it worked nonetheless. If you have time, please consider leaving a rating and review on the Joomla Extension Directory for JFBConnect, or our support. It's certainly not required, but very appreciated!
extensions.joomla.org/extensions/social-...ook-integration/7215
Best of luck to you and your site,
Alex