WP Bulletin Board (WPBB) is an easy to use forum for your WordPress site with Facebook and Twitter features.
Your newly created forum is viewable by visiting the page it uses. The page will be called "Forum" by default and depending on your permalinks settings will have a url like mywpsite.com?page_id=95 or mywpsite.com/forum etc.
I always have and will provide free support for any of my plugins. If you do encounter any problems when installing this plugin I'll be glad to assist you as well.
None whatsoever. When you deactivate the plugin, WPBB will stop working and will notify you that the plugin is deactivated. This can be disabled by deleting or editing the page that WPBB creates for you. When you reactivate the plugin, WPBB resumes as normal. If you do decide to delete the plugin, everything is removed for you, so do take care that you don't remove the plugin by accident.
Firstly always download the plugin again as the plugin is constantly updated. It is likely the problem you're having has been fixed already. If that doesn't work, create a topic here: http://wordpress.org/support/plugin/wp-bulletin-board
It is likely that you are updating a forum with roles that no longer exist. Go to your admin dashboard -> WPBB -> Tools -> Refresh Roles. Use this tool whenever you add, change or remove roles. Roles are like the ranks or capabilities that users have, e.g. subscriber, author, administrator, etc.