How to track down this SQL error?

I notice in my error log file the following:

[04-May-2013 10:17:02] WordPress database error You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ” at line 1 for query SELECT SQL_CALC_FOUND_ROWS wp_rb_posts.ID FROM wp_rb_posts INNER JOIN wp_rb_term_relationships ON (wp_rb_posts.ID = wp_rb_term_relationships.object_id) WHERE 1=1 AND ( wp_rb_term_relationships.term_taxonomy_id = 6861 made by require(‘wp-blog-header.php’), wp, WP->main, WP->query_posts, WP_Query->query, WP_Query->get_posts

I have no idea what is causing this error. How can I best debug the problem? (google searching didn’t help me much)

Thanks.