cannot open multi-query plan as cursor

Hi,
I try to run a function which calls this query: (RH7.1 and Cygwin;
PSQL7.3.2; Odbc; Windows (XP&ME&9x) clients)
----
select distinct productid, quantity, date, (select dir from t_changes where
id=changeid) as dir from t_stockchanges join t_prod_in_pgr using
(productid) join t_productgroups on (t_productgroups.id=productgroupid)
where productid in (select productid from t_prod_in_pgr where productgroupid
= '2') and (date between ' 2003.06.07' and '2003.08.07') and
(t_stockchanges.stockid in (1)) and (productid in (select id from t_products
where id in (select productid from t_prod_in_pgr where productgroupid in
(30,26,4,2,6,7,24,25,21,29,17,23,27,28,20,22)))) and
(t_stockchanges.changeid in (7,3)) and ((prooftype = 'INV'and proofid in
(select id from t_invoices where partnerid in
(31,7,18,21,33,8,19,27,28,9,12,32,10,24,16,13,29,26,22,20,14,23,25,17,15,11,
30))) or (prooftype = 'DSPN'and proofid in (select id from t_dispatchnotes
where partnerid in
(31,7,18,21,33,8,19,27,28,9,12,32,10,24,16,13,29,26,22,20,14,23,25,17,15,11,
30))));
---

When I copy it into the console (psql) it runs well, but from function it
sends an error:
ERROR: cannot open multi-query plan as cursor

What does it mean? Could anybody help me?

Thanks a lot,

-- Együd Csaba

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