[Frumph]

Notice: bbp_setup_current_user was called incorrectly. The current user is being initialized without using $wp->init(). Please see Debugging in WordPress for more information. (This message was added in version 2.3.) in /wp-includes/functions.php on line 3049

[Robin W]

We could do with a bit more information than just the error!

Have you just installed, or is this an existing bbpress site that has gone wrong?
What were you doing at the time?
Have you added any plugins or done any upgrades recently?
Does it work at all?
Does you site work but bbpress not?
What versions of bbpress and WordPress are you on?
what theme?
what plugins are you using?

[Stephen Edgar]

This is a known issue, please see bbPress#2412 and we need to wait for the issue to be fixed upstream WordPress Core per WP#24169