admin/reports/visitors

Drupal 6.13, Gnu/debian Lenny + postgresql + apache + php5

on this page and only this page i have:

* warning: pg_query() [function.pg-query]: Query failed: ERREUR: la fonction concat(int_unsigned, character varying) n'existe pas LINE 1: SELECT COUNT(DISTINCT(CONCAT(uid, hostname))) FROM acce... ^ HINT: Aucune fonction ne correspond au nom donné et aux types d'arguments. Vous devez ajouter des conversions explicites de type. in .../includes/database.pgsql.inc on line 139.
* user warning: query: SELECT COUNT(DISTINCT(CONCAT(uid, hostname))) FROM accesslog in ...modules/statistics/statistics.admin.inc on line 87.

all others pages are OK.