bbPress.org

something has changed !

Have you added any functions, or might be a plugin

bbPress is tested with wordpress default themes. It maybe a conflict – you need to check plugins and themes

It could be a theme or plugin issue

Plugins

Deactivate all but bbpress and see if this fixes. if it does, re-enable one at a time to see which is causing the error.

Themes

If plugins don’t pinpoint the problem, as a test switch to a default theme such as twentytwelve, and see if this fixes.

Otherwise try adding this at the bottom of your functions file

function change_reply_order() {
$args['order'] = 'ASC';
 return $args;
}
add_filter('bbp_before_has_replies_parse_args', 'change_reply_order');