Aggregate function problem in VB6

Hi,
I have encountered a problem with following query run over ODBC in MS VS 6.0
SP5 in DataEnvironment designer:

"SELECT SUM(field1) FROM table1;"
field 1 is of type INT4.

There is "E_FAIL" error message.

I use:
    PostgreSQL 7.1 on OpenBSD 2.9
    ODBC PostgreSQL 7.01.0005
    MS Visual Studio 6.0 SP 5
    MS ActiveX Data Objects 2.6 Library
    Microsoft OLE DB Provider for ODBC Driver

Other aggregate functions work ok.

Thanks
    Przemek Wieclawek.