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When you cannot take a picture, and the error message references "Write protection", that means the picture is registered in the camera's optical sensors, but cannot be stored on the memory card.
Write protection means a switch has been thrown into a position on the memory card, which indicates to the circuitry of the memory card reader, that writing to the memory card is forbidden.
Most memory cards have a little switch on them, and next to it the writing says 'LOCK' and has an arrow-head pointing in one direction.
Remove the memory card from your camera. Slide the 'LOCK' switch in the direction opposite to the direction the arrow-head indicates, to un-lock and allow writing to the memory card.
Put it back into the camera. Take a picture! it ought to work then.
Let me know how it goes, please. I'd like to know whether my advice helped with the case. Thanks.