I've had this with 4gig SD's ...
Its your reader ... many have a 2gig limit, and most wont read SD-HC high capacity cards ...
Buy a cheap USB pen type reader with a SD slot in it, that is SD-HC compatible (about £6 on ebay).
I notice many SD cards =>4gig now come with readers, probably becuase lots of others are having this problem and returning the cards.