Thought this might deserve it own thread as it's likely quite a few Sony users bought these cards during the black friday promotions and are not yet aware of the issue. The problem is with Sandisk 64gb Extreme Pro 95mb's UHS-1 SDXC & Sandisk 128gb Extreme Pro 95mb's UHS-1 SDXC memory cards in Sony a7 III, a7R III & a9 being used in card slot 1 resulting in this warning: “Unable to read memory card. Reinsert memory card. Slot 1" There have been some reports of older Sony camera bodies having the same issues. This is only a problem since Sandisk made a change to these memory cards a couple of months ago by changing the controller in the cards so only effects newer produced cards. At first many people seemed to believe that was an issue with Sony firmware, as they released new firmware around the same time. I have spoken to both Sony and Sandisk and both have said that this is due to the change that Sandisk has made to the cards and regardless of what firmware the camera has this will be an issue. Reported bad batch numbers thus far include: 128 GB Sandisk Extreme Pro UHS-I – batch 766G 64 GB Sandisk Extreme Pro UHS-I – batch 838G, 839Z This is only an issue when using the cards in slot 1, they will work in slot 2. Formatting the card in camera or in another device makes no difference. I have also had the same issue with 256gb Sandisk cards but have now returned theses and didn't keep a record of the batch number. Sony users might be better to avoid purchasing new Sandisk cards for the time being.