#40 db error in phonelog with postgres

Warning: PostgreSQL query failed: ERROR: Function
'concat(varchar, unknown, varchar)' does not exist
Unable to identify a function that satisfies the given
argument types You may need to add explicit typecasts
in
/usr/local/phpgroupware/phpgwapi/inc/class.db_pgsql.inc.php
on line 96
Database error: Invalid SQL: SELECT pl_id,
pl_callfrom_id, pl_callfrom_txt,
CONCAT(account_firstname, ' ', account_lastname),
pl_calldate, pl_status, pl_desc_short FROM
phonelog_entry, phpgw_accounts where
pl_callfor=account_id AND account_id=595483 AND
pl_status >= 1 ORDER BY pl_status DESC
PostgreSQL Error: 1 (ERROR: Function 'concat(varchar,
unknown, varchar)' does not exist Unable to identify a
function that satisfies the given argument types You
may need to add explicit typecasts )

Session halted.