How To Remove Write Protection From Pen Drive?

1. Go to run, type regedit and press enter.
2. Navigate to the path:
HKEY_LOCAL_MACHINESYSTEMCurrentControlSetControlStorageDevicePolicies
If the registry key StorageDevicePolicies does not exist, you will need to create it manually.
3. Highlight StorageDevicePolicies, and then create a New DWORD (32-bit) Value named as WriteProtect.
4. Double click the key WriteProtect in the right window and set the value to 0 in the Value Data Box and press OK button
5. Restart your computer and see if this help

If there is no important file, try to format
Click on Start.
Type diskmgmt.msc in Run.
In the disk management window, select the pen drive, right click on it and click on Format. Now choose the File System and Allocation Unit Size.
Click on OK.
or
1. Start > search bar -> CMD and press enter
2. type< diskpart
3. type< list disk
4. type< select disk # (# is the number of the USB key)
5. type< attributes disk clear readonly

perhaps this hot-fix can help also
http://www.makeuseof.com/answers/remove-write-protection-sandisk-pen-drive/
perhaps take ownership
http://www.rizonesoft.com/2011/ownership-shell/
You can find two reg files below if you are on xp or vista
http://www.mydigitallife.info/how-to-disable-write-access-to-usb-hard-disk-and-flash-key-drives/