SQL Error on main forum list page
The error message is saying that the user you set in your settings.php file doesn't have access to the database, which could happen because the password you wrote in that file is not the correct one.

Any Drupal module that accesses the database is using the database API, which doesn't require any username or password, as those are taken from a file that Drupal reads during its bootstrap.
The Forum and the Advanced forum modules are not an exception. If you are getting that error, it means there is an error with the settings.php file, or a problem with the database server.