"Multiple steps operation" error

I found a lot of postings about the same error message, but not one
that helped me...

First of all the scenario:

Windows 2000 Professional
Delphi 5.01 Enterprise (patched, including adoexpress)
Oracle 8.0.6
Table:
CREATE TABLE TESTE (
FIELD1 VARCHAR(4) NOT NULL,
FIELD2 VARCHAR(10) NOT NULL,
FIELD3 VARCHAR(30) NOT NULL,
FIELD4 VARCHAR(100) NOT NULL,
FIELD5 VARCHAR(2));

I have a COM+ application and in same point of application the server
DLL executes a SELECT statement like this one using a TADOQuery:

SELECT FIELD1, FIELD2, FIELD3, FIELD4, FIELD5,
  RPAD(' ',100) AS FIELD6,
  RPAD(' ',150) AS FIELD7,
  RPAD(' ',250) AS FIELD8,
  SYSDATE AS FIELD9
FROM TESTE;

I use these constant fields 'cause I need to edit that query and send
the data to the client application.

The query is in cached updates mode, and I don't perform an
ApplyUpdates, 'cause the information is not relevant to be stored in
database fields.

But when I execute:

qryTeste.Edit;
qryTeste.FieldByName('FIELD6').AsString := 'Some string around 50
chars';
qryTeste.FieldByName('FIELD7').AsString := 'Some string around 120
chars';
qryTeste.FieldByName('FIELD8').AsString := 'Some string around 200
chars';
qryTeste.FieldByName('FIELD9').AsDateTime :=
qryAnother.FieldByName('ANOTHERDATEFIELD').AsDateTime;
qryTeste.Post;

Debbuging the adodb.pas, into UpdateData function, called by Post
method, the update of FIELD6 is generating a 'Multiple-step operation
generates errors...'.

Why??? What am I doing wrong?

Thanks in advance...

Zed.