I will restate the issue to you again.
1. If a new user registers on the website, he is able to do it successfully.
2. When the user tries to login for the very first time via joomla/CB nothing happens. No Error Nothing.
3. If this user navigates to phpbb3 (hhtp://www.tag-india.in/bpug) and tries to login, he is able to do so successfully. Now being logged into phpbb3 if the user navigates to joomla, he is logged in there as well.
4. Now after logging out if he tries to login again he is able to do so from both joomla and phpbb3. Everything works fine.
This essentially means that problem is only for new registration right now and that too only if the user tries to login into joomla for the first time. This has definetly something to do with CB? We cannot disable phpbb3 plugin it is just as important like CB.