Subject RE: [firebird-support] This column cannot be updated because it is derived from an SQL function or expression.
Author Alan McDonald
> I have found the problem. I had a Before-Update-Trigger in which
> assigned a value to the OLD context.
> But it's a quite misunderstanding error message.
> Regards
> Guido

OLD context variables in before triggers and NEW context variables in after
triggers are now read-only

It's all in the relase notes.