parameter passing from java program

Dear Sirs,

I am spending about 10 hours on little problem: to pass a parameter (text)
to a PostgreSQL (v. 8.1 on Win2000). The
relevant code is:

java side:
private CallableStatement cs;
cs = conn.prepareCall(INSERT_CONGRESSO);
cs.setString(1, itemCongresso.getCongresso()); //return a String
cs.execute();
...
public static final String INSERT_CONGRESSO = "{SELECT ins_congressoa(?)}";

PostreSQL side:
CREATE OR REPLACE FUNCTION ins_congressoa(congresso text)
RETURNS void AS
$BODY$INSERT INTO "Congressi" ("Congresso") VALUES ($1)
$BODY$
LANGUAGE 'sql' VOLATILE;
ALTER FUNCTION ins_congressoa(congresso text) OWNER TO postgres;

With Pgadmin the function work fine, but from java program does not. WHY?

Thank you.

Domenico