I had the same problem ( have been using 1.41 to play Viva Pinata).
As has been said, the rom was the problem.
If you don't want to upgrade the firmware, don't use a patched rom.
As soon as I found a clean rom, the cheats option worked just fine.
Haven't tried 1.43, which apparently corrects for Viva Pinata and works with CT, will try this tonight.
Update: Yep, working fine with 1.43