I can't seem to able to format my PNY 32 GB SD card

When I go to Disk Utility and try to erase it gives me error: Unmounting disk, Couldn't modify partition map and operation failed

I successfully unmounted disk2 (the SD card) via terminal but when trying to erase it it shows error -69877 couldn't open device

I also tried command sudo dd if=/dev/zero of=/dev/disk2 bs=1024 count=1024 but it shows permission denied

System: OS X El Capitan 10.11.6

Can you help please?

  • Do you have another SD card you can try? SD cards are known for a high failure rate, so let's see if we can diagnose the issue.
    – Allan
    Apr 5, 2020 at 2:58
  • No I don't.. although it looks like I will need to get a new one. But it's weird as the SD card was working until yesterday morning. It got corrupted after attempting to delete pictures manually in pc. Apr 5, 2020 at 15:14
  • I’ve had this happen to me many times - once when I was in the middle of a shoot. When you get your new SD be sure to come back and post an answer or update the question. I’ll upvote
    – Allan
    Apr 5, 2020 at 18:43

1 Answer 1


I had the same problem, but per this Mac Forum discussion, SanDisk Micro-SD to SD Adapters has a 'Lock" slider that is easy to miss. After unlocking the card, I was able to reformat the microSD card with no problem.

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