Format usb drive (dmg is on - and show read only)
i remember this from a few years ago -- there were a lot of these slipping into RO mode.  here is a forum talking about it: http://forums.sandisk.com/t5/All-SanDisk-USB-Flash-Drives/Sandisk-cruzer-16GB-became-read-only/td-p/255218/page/2

with no real solution.  it is a hardware issue, regarless of operating system etc.