All of a sudden my Garmin Edge 800 has stopped reading the maps on the SD Card (GB Discoverer 1:50K). There doesn't seem to be a problem with the SD card because they are read by Base camp, and the Mac. When I go into the Map option in System settings, it doesn't recognise the SD Card. I have French maps on an SD card and these are picked up fine, so it's not a problem with the SD card reader. The software for the device is up to date. Does anyone know what the solution might be?