at and fat16 are the same thing. So it should be working.
Its possible that your SD card isnt compatible with the wii. What size is it? The wii only supports SD cards up to 2 gigs.
Go to parental controls on the wii setting. When it asks for your pin press "I forgot" and then it will ask you you question also press "I forgot". Then a screen will come up telling you your confirmation number. Write down the Confirmation number and go to http://wii.marcansoft.com/parental.psp...