Follow the following solutions to fix the A6300 Memory Card error - image database file not ready:
Solution 1: Select Setup and choose Recover Image DB and try that.
Solution 2: If above solution fails, then Switch OFF the camera and again Switch ON your camera and format it before camera try to read it.
Solution 3: If that also does not work, then insert the card into card reader and connect it to PC/Mac take backup of everything and delete everything from it. Now insert the card in camera, it will now give the option to format.
Solution 4: It might be possible that the card you trying is locked. There will be small tab just on the side of the card, where you can see the word LOCK next to it. Just slide the tab towards the opposite side and try again.
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Following the solutions will definitely help you in solving the above problem.