warning at poll result page

I get this warning messages if try to go to polls result page:

* warning: pg_query(): Query failed: ERROR: column "c.value" must appear in the GROUP BY clause or be used in an aggregate function in /usr/share/drupal5/includes/database.pgsql.inc on line 125.
* user warning: query: SELECT n.nid, n.title, p.active, n.created, c.value AS votes FROM node n INNER JOIN advpoll p ON n.nid = p.nid INNER JOIN votingapi_cache c ON n.nid = c.content_id WHERE n.status = 1 AND c.tag = '_advpoll' AND c.function='total_votes' AND c.content_type='advpoll' GROUP BY n.nid, n.title, p.active, n.created ORDER BY n.created DESC LIMIT 15 OFFSET 0 in /usr/share/drupal5/includes/database.pgsql.inc on line 144.

I use postgresql database.