Disk Utility Cannot erase USB Drive (Error: -69877: Couldn't open device) I have a PNY 128gb flash drive that I can no longer modify (can't delete files). I've tried to reformat it using Disk Utility but I get the following message and my usb is unmounted:



I've followed the solutions found from these two postings with no luck.

Disk Utility cannot erase

Disk Utility won't erase

When I type in 'diskutil eraseDisk free EMPTY /dev/disk2'
into terminal my usb is unmounted just like before and I get this message:



Any ideas on what I can do to erase and reformat my USB drive? Any help is much appreciated. Thanks!
Before trying anything more radical, do make sure (if you're using a microSD-SD adapter) that the adapter isn't write protected / locked. D'oh! It can be missed easily.