What happens if you run your script until it fails (committing just
before the failing command), and then issue:

select * from corresp
where
NAME is null or
ACCOUNT is null or
SUBACCOUNT is null
or CREF is null

Does that query return any rows? If not, what happens if you do

select NAME, ACCOUNT, SUBACCOUNT, CREF
from corresp
group by NAME, ACCOUNT, SUBACCOUNT, CREF
having count(*) > 1

Set

--- In IBObjects@yahoogroups.com, "Riho-Rene Ellermaa" wrote:
>What is the Null segment - does it mean that no field can contain
>NULL value?
>When I look at the data, I don't see any NULL values. Some fields
>are just empty, but none show <Null>. When I deleted all rows before
>running script, then the error dissapeared.