D7 and DOA 4.0.6.2

I'm sorry but this problem still occurs to me.

with the following SQL statement:

select numField
from Tbl1
union
select numField
from Tbl2

and using the 'numField' TField created in the OracleDataSet, I get the error message in the subject.

Neither "event 10499" works in Oracle 9.2!
More, in Oracle 10g "event 10499" is no more supported!!
The only way is to delete the TField and access the 'numField' field via FieldByName method.

In a past message you said that in DOA 4.0.6.2 this problem should have been fixed.
Maybe the problem raises because of the "select union" statement? Anyway with Oracle versions before 9.2.0.5 this error never occured.

Any idea?
Thanks a lot.

Massimo