Did you already try tot format the card inside the camera? It might help.

Rutger

You may have a bought a fake compact flash card of which performance and
reading problems have been widely reported ( Check on this link to get the
skinny: http://martybugs.net/articles/fakesandisk.cgi )
Fortunately, some CompactFlash and SD companies place a unique identifier on
the card - a card series number, for instance - that is a reliable
descriptor of the key components in the card, as long as you know how to
interpret the identifier.

If you used your CD card heavily, the usefull lifetime may have been
reached. CompactFlash and SD cards are designed to automatically and
transparently map out memory cells that go bad, or in some cases when they
reach a predefined limit of erase/write cycles. Cards should continue to
function some time after a few cells have expired, but may experience
problems being read by other systems (e.g. computer)

Try to update the camera's software and reformat the card only in the
camera. Cameras don't write their stream of zeros and ones randomly. All
digital SLR and compact cameras use the FAT file system as the basis for
placing photos on a card and keeping track of the location of those photos.
This means the cards themselves have to be FAT-formatted, regardless of
whether they're hard drive or flash memory storage media. Cards with
capacities over 2GB must be formatted FAT32, a newer variant of the FAT file
system that is not widely supported in older digital cameras (though most
camera models that accept CompactFlash or SD introduced from roughly 2003
onwards should be FAT32-capable).