This message pops up when the camera does not detect a memory card. Please ensure you have inserted a memory card properly into the camera.
If the memory card is inserted properly into the camera and the message still appears, please attempt to format the memory card. You can follow the instructions located here to properly format your memory card.
After formatting, if the camera still does not detect the memory card, please try a spare class 10 memory card in the camera if available.
Should it work with the second memory card, then your first memory card may be defective.
If the camera does not work with the second memory card, please contact DOD Tech support for further assistance.