phpBB module with two database

Is possible to install drupal in one database (with his username and password) and phpBB in another database (with other username and password), using phpBB module?

In my "configuration.inc.php" file, i've add this:

$db_prefix = 'phpBbDatabaseName.phpbb_';

instead of

$db_prefix = 'phpbb_';

but i've got this error:

user warning: Access denied for user 'drupalDBuser'@'%' to database 'phpBbDatabaseName' query:
SELECT user_unread_privmsg FROM phpBbDatabaseName.phpbb_users WHERE user_id = 1 in
/www.myWebSite.com/htdocs/includes/database.mysql.inc on line 172.

Can you help me?