i cant understand why noone read the installation instructions...
from plugin page :
Once you have your WordPress and phpbb forum set up, download and install the WP phpBB Bridge plugin and activate it. (Make sure you use the same credentials for both WordPress and Phpbb Admin user: Name/email/pass)
Note: There is a difference between activating the plugin and activating the bridge. You must activate the plugin first in order to see the WP phpbb widgets, but DO NOT activate the bridge just yet.
Go to menu Appearance/widgets. (You will find 4 new widgets)
Drag & drop the widget called "phpbb3 Users Widget" to the widget area of your template to activate it.
If you want you can activate all widgets but make sure that you fill the form "forums" with the id's of phpbb forums you like, to get topics from in widget "Phpbb3 posts widget"
Go in menu: «WP phpBB Bridge» and complete the paths for config.php and ucp.php.
Typically it should be similar to this depending on your file structure:
Path to config.php: /home/content/html/wordpress folder/forum folder/config.php
URL to ucp.php: http://YOUR-WEBSITE.com/phpbbfolder/ucp.php
Now activate bridge.
That's it !! You're good to go...
you can also see how to install it in this video :
If you've completely botched this up, there are a few things you can do:
1.) The easiest method is to go to your website FTP, locate your wp-content folder > plugins and completely delete your PHPBB bridge plugin
2.)If you need immediate access to wp-admin then all you need to do is FTP into your WordPress plugins directory and rename the wp-phpbb-bridge plugin folder to something else. You'll be able to access wp-admin once again.
The problem however is that the bridge function of the plugin is still enabled in MySQL... Here's the fix for that...
Login into phpMyAdmin from your CPanel and open your WordPress database. Search for wpb_active and select all the DB tables before clicking Go. You'll now see the row wpb_active, click on edit. Change both "yes" values to no. You now have your wp-admin back!
hope this helps and isn't too confusing. Good luck!