If you get the titled error (“Media is write protected”) out of nowhere and it’s driving you nuts, try the following:
Hit Windows-R and bring up the Run dialog box.
Type “cmd” in the box and watch the DOS-like screen pop up.
Type “diskpart” in the DOS-like window.
Next, select the volume you’re having troubles with (i.e. “select volume C”).
After it’s been selected, type:
“attributes volume clear readonly”
Give it a second, and that should do it. You should now be able to set permissions as you like on the selected volume.