Authenticate in WordPress and phpBB at the same time
To uninstall, you have a few steps to make
Go the the Plugin options, revert the "auth mode" to "DB" and not "wpbb" If it doesn't work go to the ACP in General -> Client communication -> Authentication
Then go to the wordpress control panel and disable the plugin.
The last step is then to go with FTP in the PHPBB folder and rename the file "common.php" to "common.wp.php" and the file "common-orig.php" to "common.php".
Your configurations should be separated again