Some SD cards and USB sticks have write protection switches. When enabled they prevent files from being deleted, or any new files being written to the device. It also stops you from accidentally formatting the card or stick.
Occasionally, you’ll find that an SD card or USB flash drive will refuse to format and Windows will tell you that it is write protected, even though there is no switch, or the switch is set correctly to allow the device to be written to.
Typically, you can read the files which are already stored on the drive, but you can't delete them (they sometimes seem to delete ok, but the next time you check, there they are again!).
Here are a couple of ways you can try to format the drive and remove the write protection. Bear in mind that there is no guarantee that they will work for you: your USB flash drive or SD card may be corrupt or physically broken and no utility or low-level formatting tool will make it work again. The only solution in this case is to buy a new drive. (See also: Recover deleted files for free: recover lost data.)
How to erase a write-protected USB drive in the Registry using Regedit.exe
In any version of Windows from XP onwards, run Regedit.exe (searching regedit will usually show the program at the top of the list).
Navigate to the following key:
Double-click on the WriteProtect value in the right-hand pane of Regedit.exe. Change the Value data from 1 to 0 and click OK to save the change. Close Regedit and restart your computer. Connect your USB drive again, and you should find it is no longer write protected. You can now format the drive as normal by right-clicking on it in My Computer and choosing Format.
If you can’t find StorageDevicePolicies, you can try creating a key by right-clicking in the white space in the Control folder and choosing New -> Key and carefully entering the name.
Now double-click on the new key (folder) and right-click once again and choose New -> DWORD. Name it WriteProtect and set its value to 0. Click OK, exit Regedit and reboot your computer.
If this method doesn’t work, try the following:
Removing write-protection using Diskpart
With your USB drive plugged in, launch a command prompt. Do this by searching for cmd.exe in the Start menu (or Start screen in Windows 8). In Windows XP, click Start then Run, and type cmd.exe in the box.
NOTE: you may need to run Cmd.exe with administrator privileges if you see an “access is denied” message.
To do that, right-click on the shortcut and choose Run as administrator. In Windows 8, simply choose Command prompt (admin).
Now, type the following, pressing Enter after each command:
select disk x (where x is the number of your USB flash drive – use the capacity to work out which one it is)
attributes disk clear readonly
create partition primary
format fs=fat32 (you can swap fat32 for ntfs if you only need to use the drive with Windows computers)