with 1.6.7 i'm getting the following error message:
failed connection [[unixODBC][Driver Manager]Invalid string or buffer length] (0)

I'm trying to use unixODBC with postgresql module. the username and password is supplied in the odbc.ini.
item key: db.odbc.select[dbsize_pdms]
additional parameters: DSN=pgdb1\nsql=SELECT pg_database_size('pdms');

of course, this query does work from the isql cli utility.

and also please take a look at this forum thread:
http://www.zabbix.com/forum/showthread.php?t=10964