I tried 3 other 64GB SanDisk ExtremePro UHS-I cards in slot 1 with no issues, my issue is limited to 2 of the 3 128GB cards I tried. However my original 6 month old 128GB card works just fine in slot 1. The replacement card refused to work in slot 1, just as the 1st new one did. Put it into slot 2 and was able to format, take photos and transfer again with no problem. Now that I knew the replacement 128GB card was working OK, I again put it in the A7III slot 1 and got the same error message. So I tried the replacement card in the UHS-II slots of my Panasonic G9 And Nikon D500, where I used the original 128GB UHS-I card with no issue, and the new replacement card worked just fine in both, I was able to format, take photos and transfer no problem. Just like with the new 1st card when I put the card in slot 2 of the A7III, I was able to format it and take photos, however when I put the card back into slot 1, the same error message appeared. Received the replacement 128GB card on Friday and when put in slot 1 of the A7III it showed the same message as before. I assumed the card was bad, so I returned it.

But as soon as I put it in slot 1, I got the same error message and the camera stopped working. Put the card into slot 2 and I did not get the screen and was able to format the card and take photos with it in slot 2. So I removed the card and the camera was back to normal. Slot 1.” You cannot format the card or operate the camera when this message is visible. I put it into the Slot 1 and immediately got a black screen saying “Unable to read memory card. Wanted a backup 128GB UHS-I card so I ordered the same model as the one I have and it came last week. Both cards worked just great I write raw, and the small amount of video I do, to the 128GB card in slot 1 and Ex. I only use SanDisk ExtremePro SD cards with great success and had both a 128GB and 64GB R95/W90MBs UHS-I V30 card, that are about 6 months old, that I put into the Sony.

Received my Sony A7III about 3 weeks ago.

How to format sd card sony a7iii