How to unlock memory card for camera

Have a look at the (presumably SD) card and see if there's a small lever on it. That will have set the card to read only.

Alternatively, if this card has not been used in this camera before and is SDHC make sure that the camera takes HC (older cameras may be limited to 2gig cards and lower).

OR -- if the card has been used in a different camera before, it may need formatting using your camera before it will work.