Nintendo DSi error message

Hi everyone!My son's DSi keeps displaying the following error message:

''An error has occured. Press and hold the POWER button to turn the system off. Please refer to the Nintendo DSi Operations Manual for details''.I do not have the manual, cannot go into 'settings', tried taking the battery out and putting it back in, but it just won't reset!!Can anyone help please??

What card is inserted in the DSi?