Calibre won't detect the SD card in my Kobo H20

Hi

I have a Kobo H20 with an SD card. Up until a week or so back Calibre on my pc detected both the main storage and the SD card fine but now Calibre doesn't see my SD card. The card works fine in the Kobo and Calibre on my husbands machine sees both the main storage and the card, its just a problem on my pc.

Windows sees both main storage and SD Card its just Calibre that doesn't. Does anyone have any ideas why Calibre doesn't see it anymore?

I'm running 2.5.3