PHP BB Single Sign on plugin not working fully

Using version 3.3.1 of wordpress and PHP BB. The issue is that the plugin is showing all things fine in the setup once the database is same. But while using it following issue is there:
If I login into the WP, automatically logged in to PHPBB and same for logout. But if I perform these actions in PHPBB it is not doing the same in WP. i.e. If I log out from Phpbb I am not logging out of WP and same for log in.
Also the userID which is registered in WP is allowed to register in phpbb but not letting login afterwards.
Can someone let me know how to have this thing working. An alternative of the same can be replacing top right three links in PHPBB for registeration / login / logout etc to be replaced with the similar links from WP function.
I can not do the same myself as not a programmer but would prefer if this can be done easily.