> When I call this stored procedure, the result value CODE is always equal to NULL !

How do you execute this procedure ? Do you use IBConsole ?
If yes, then you should know that EXECUTE PROCEDURE command
does not work in IBConsole - it looks like you get <null> result,
but the procedure is not executed at all.
Try to execute it as select procedure - you will get error message,
but then correct answer.

Ivan
prenosil@...