EK7000 - Format Problem

I'm having an issue with one of my EK7000's. I have five of them, so know my way around the device. The firmware version is FX180911V6.

The problem seems to be with the formatting of the SD card. The problem camera will format the card and take videos and photos with seemingly no problem. However, when I eject the card and put it into my Macbook to get at the content, the Mac says the card is not readable - it doesn't do this with my other 4 cameras. If I then put the card into any of my other EK7000's, it will flash Card Error.

I then tried formatting the card in a 'good' camera before moving it to the 'problem' camera. when the problem camera is turned on, I get the message to format it as 'the file system format does not meet the requirements'.

I've tried using different cards (which all work fine in my other 4 cameras) but the common denominator seems to be the this one particular camera and the way/manner it formats.

Extensive trawling and goggling has only led to to trying a U3 card (the others are U1) but this is still not fixing the problem, rendering the camera useless.

Does anyone have any tips?