If it's a DS model, not an MSO, then the decoder does work, even on the latest version. Check that you didn't include dashes, as Daruosha said, and that you don't have any typos.
Note that if you fail to enter a valid code too many times, then the scope will temporarily lock you out and entering any code, even a correct one, will fail. Unfortunately, the "temporary" period is 12 hours of the scope being on. Since the scope doesn't have a real-time clock, it must be left on for 12 hours to clear the lockout.