user error: message

I have posted a page in a book with a user successfully. Now when other users see my post, they get this message on the browser:

warning: pg_query(): Query failed: ERROR: column "v.weight" must appear in the GROUP BY clause or be used in an aggregate function in /var/www/localhost/htdocs/drupal/includes/database.pgsql.inc on line 104.

user error:
query: SELECT v.mid, v.vote, MAX(r.value) AS value FROM moderation_votes v INNER JOIN moderation_roles r ON r.mid = v.mid WHERE r.rid IN (2, 3) GROUP BY v.mid, v.vote ORDER BY weight in /var/www/localhost/htdocs/drupal/includes/database.pgsql.inc on line 121.

Any reason why they would get this?

Thanks!