I cannot view recently added issues, I receive the following database errors:

Warning: pg_query() [function.pg-query]: Query failed: ERROR: syntax error at or near "ON" at character 24 in /SITE_PATH/httpdocs/includes/database.pgsql.inc on line 125

Warning: ERROR: syntax error at or near "ON" at character 24 query: SELECT COUNT( DISTINCT ON (n.nid) n.nid) FROM node n INNER JOIN project_issues p ON p.nid = n.nid INNER JOIN node_revisions r ON r.vid = n.vid INNER JOIN users u ON p.assigned = u.uid WHERE n.status = 1 AND ((p.pid = '14')) AND ((p.sid = '1' OR p.sid = '2' OR p.sid = '4')) in /SITE_PATH/httpdocs/includes/database.pgsql.inc on line 144

Warning: pg_query() [function.pg-query]: Query failed: ERROR: SELECT DISTINCT ON expressions must match initial ORDER BY expressions in /SITE_PATH/httpdocs/includes/database.pgsql.inc on line 125

Warning: ERROR: SELECT DISTINCT ON expressions must match initial ORDER BY expressions query: SELECT DISTINCT ON (n.nid) n.nid FROM node n INNER JOIN project_issues p ON p.nid = n.nid INNER JOIN node_revisions r ON r.vid = n.vid INNER JOIN users u ON p.assigned = u.uid WHERE n.status = 1 AND ((p.pid = '14')) AND ((p.sid = '1' OR p.sid = '2' OR p.sid = '4')) ORDER BY n.changed DESC LIMIT 20 OFFSET 0 in /SITE_PATH/httpdocs/includes/database.pgsql.inc on line 144

Please help :)
PostgreSQL database 8.1.11
Web server Apache/2.0.55 (Ubuntu) mod_python/3.1.4 Python/2.4.3 PHP/5.1.2 mod_perl/2.0.2 Perl/v5.8.7