Huge mistake on a customer billing procedure.
That procedure was generating a file for automatic billing requests from our customer bank to his customers banks.
That procedure was shifting the bank coordinates by one byte right making all payment requests invalid and rejected.
That month the customer got nothing from invoices (more or less 80k euros).
Side note; only one payment was accepted because the guy entering the invoice on the system shifted the bank coordinates by mistake, so the procedure fixed it.

:/