Running buddypress? Are you getting a debug notice like this:
The current user is being initialized without using $wp->init()
and you cannot figure out where it is coming from ?
Most likely one of your plugins is calling a user related wordpress function a bit early (see wordpress action sequence). You could try deactivating them until the debug message goes away. The last plugin deactivated will be it. Let the developer know because his/her code may not be quite working the way it was intended to.
eg: current_user_can() or possibly wp_set_current_user()
These need to be used after the init action. The plugin or theme might have something like
add_action ('plugins_loaded', 'some_function');
The action should be added later, when the current user has been initialised.
add_action ('init', 'some_function');