Downloading photos from a card received the message "macOS can't repair the disk "LUMIX"
I've just bought a 64GB SanDisk Extreme PRO SDXC UHS-I card (speed up to 200 MB/s) to replace a few elderly 8GB (speed up to 15 MB/s) cards for use in my Lumix TZ90 camera. I formatted the card in my camera and then took a few photos, checking in the viewfinder that they had been recorded on the card. I removed the card and inserted it in my admittedly rather old Bytestore card reader which I attached to my iMac using the UHB cable and was greeted with the message above on the screen. I tried the same exercise with one of my old 8GB cards and it worked perfectly without any message. I recently returned from a birdwatching trip to Colombia where I had taken numerous photos on another new card which I had formatted and checked the photos on the camera etc and lost the lot when I tried to download them to my iMac so I'm very twitchy about not wanting to go through that dreadful experience again. Has anyone any suggestions of a solution please?
iMac 21.5″, macOS 10.13