At the very least, do a low level format of the card. For a CF card, this must be done in a computer, for a SD card, there is a low level format option in camera. Any bad memory cells on the card will periodically have a image saved to them, and that's what you will see.
I'd just return the card to the manufacturer for replacement. The bad memory cells may multiply, or a much wanted shot will be the one to get damaged.
The card controller tries to write files evenly over the memory bloks in the card, so its a periodic thing. Depending on how many shots you take, and how large the card is, it might only happen every 6 months, or it might hit you frequently.