Vlad Khorsun wrote:

>> Examining the database, I can see that the
>> conversion process was a success for exceptions,
>> procedures and relations while triggers still
>> contained the intermediate (temporary) strings.
>>
>> Any new rules for Fb/2.1 ?
>
> Sure. NEW and OLD variables in AFTER triggers is read-only,
> OLD variables not accessible in BEFORE INSERT triggers,
> NEW variables not accessible in BEFORE DELETE triggers.
>

Thank you!
The word "column" in the error message may have confused me. I
didn't check the text in all triggers, but after this hint I found
the offending ones. A more specific term in "attempted update of
read-only column" would have helped.
Let the (lame) excuse be that I didn't write those triggers.
All is well (for the time being).

--
Aage J.