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Try connecting it up to your PC via a Card Reader and format it using windows and then right click on it - select "Properties" - "Tools" - "check Now" and then tick the box "SCan For and Attempt Recovery of BAd Sectors".
I've never trusted that personally - I know it's supposed to work - but I'm a bit paranoid about "hot-swap" type technology (amongs a lot of other things ) and always use the "safe route" and I've never had any media/file corruption issues with any of my external disk/usb-sticks/card-media etc. (touch wood)