>Trying SUBSTRING on Firebird thus
>P1 = SUBSTRING("ABCDEF" FROM 1 FOR 4);
>will not even compile. P1 is a previously
>defined variable (It is part of a SP.)

But what is "ABCDEF"? If it is a string, I think you should have used
single quotes - double quotes may leave FB believing it is a field name
(though I'm far from certain this is the case).

Set