Possible error messages:

* Try&Buy folder says "(no data)". You have changed the MMC card to a normal memory card. Install both AKM.sis and application.sis files to the new memory card.
* "Application Key Manager Corrupted! Exiting application". You don't have the Application Kay Manager installed in your phone. Install the AKM.sis file.
* This application key is alread in use. Please enter new key. You entered a key you already used for another application. Please buy a new key.
* You have done everything right, but can't see the application anywhere. Reboot the phone.