I have revealed the secret to make it work
It's the update you download on Online in Motorstorm that makes you unable to use it!
Delete all Game Data and Saved Data from Motorstorm and join the game again without downloading the update from online.
Well, if you wanna play online then you need to download the update i think, but then you can't use the cheat
So don't download the update, use the cheat on the main menu
and it's all unlocked!
* Updated game trainers and cheats daily
* Get notified when new cheats are added
* Request which games get new trainers
* Priority support with any problem