Database warning

user warning: 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 'DISTINCT(n.nid) FROM node n LEFT JOIN worklog_invoice wi ON n.nid = wi.nid WHERE' at line 1 query: SELECT n.title, DISTINCT(n.nid) FROM node n LEFT JOIN worklog_invoice wi ON n.nid = wi.nid WHERE n.type='worklog-invoice' AND n.status = 1 AND (wi.closed = 0 OR n.nid=11) in /var/www/localhost/htdocs/drupal/includes/database.mysql.inc on line 120.

I finally got all the tables setup and I have actually tried out workflow, but I get this message on worklog pages (not invoice pages), whenever I edit a worklog entry. I took a look at the code for workflow and I can't find a query with DISTINCT() in it. Workflow seems to work, but it is a disconcerting problem. Thanks in advance.