I have just acquired a pre-owned Nikon Coolpix 775. When I try to download images I get a 'No CF card' error message on my PC, despite there being a CF card with images on it which, when I put it in another camera, download OK. Also, the camera clicks. Why should this be and is this something to do with the 'No CF card' error message? I see other Nikon users have reported the same faults. Can anyone help?