[@netweb Keymaster 10 years, 2 months ago]

The bbp_setup_current_user issue is not caused by bbPress, bbPress alerts you of this issue though because it is important for bbPress. If you have disabled ALL your plugins and the error remains you MUST switch the theme to Twenty Thirteen (or Twenty Fourteen, Fifteen, Sixteen etc).

Once you know what plugin or theme causes the issue then you can contact the author and let them know they need to fix it and problem solved.