Blank page when subscribing (SQL error)

Hi,
When an anonymous user subscribe to a newsletter from the block, he got a blank page. Here is the error message in my logs :

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 'IN ('2')) LIMIT 0, 10' at line 1 query: SELECT node.nid, node.title AS node_title, node.changed AS node_changed FROM node node WHERE (node.status = '1') AND (node.type IN ('simplenews')) AND (.s_status IN ('2')) LIMIT 0, 10 dans /var/www/vhosts/**/httpdocs/includes/database.mysql.inc à la ligne 174.

What can be the source of this problem?
Thanks!