The IN operator

I would like to use PostgreSQL through ODBC with Delphi 5. According to the Postgre documentation the IN operator
exists,however I get the "Capability not supported!" error message after issuing the following SQL command:
 

SELECT CsoportAzonKod FROM Felhaszn_Csoport       WHERE FelhAzonKod=1 AND CsoportAzonKod IN             (SELECT
CsoportAzonKodFROM Menu_Csoport                     WHERE MenuAzonKod=1)
 

(ODBC version 6.40.00.07 - written by Insight Distribution Systems.)

Why?

Thank you

Laci