How can I fix Error: -69877: Couldn't open device after interrupted formatting process?
Solution 1:
I have run across something similar before and what I did was issue the command:
diskutil unmountDisk /dev/diskxx
What you do when you shutdown and reboot, even in safe mode is you first unmount all your disks.
Solution 2:
For anyone else who ends up on this question after searching online, be sure that you confirm that your SD card is not mounted as read-only! There is a physical tab that you may need to move:
