Hi Ross,
It's more likely that your SD card is incompatible with the Nextion display. While I was waiting for my Nextion 3.2E to get here I went to Walmart and bought a cheap 8GB SD card, when it got here, I tried to upload a file to the display and it gave me a similar error, so I used my old 16GB SanDisk card instead and it worked perfect. Both cards were formatted the same way and had the same file on them, but only the SanDisk card worked. Don't know why, I can use the cheap card on my Laptop with no problems, but the display didn't like it for some reason.
Joel
N6ALT