I believe the Sandisk comes formatted Fat32, meaning you can only add 4GB, unless you formatted it to NTFS. And the first time the device is removed from the system, that files structure is locked in. Registry edit and other fixes will not work, IMO
How to remove a write protection from your USB memory Stick if there is no Write protection ON or OFF button or tab:
1. Shutdown your computer or laptop
2. Insert USB Memory Stick into your laptop or Computer
3. Turn on computer and then immediately start pressing (F8) key then Advanced Boot Options screen will come up
4. Select Safe Mode with Command Prompt
5. After loading files if your USB Memory Stick drive letter is (G) for example then write as
6. C:\windows\system32>G: and press enter
7. G:\>format G: and press enter
8. If ask you (Y/N) then press (Y) and press enter
9. Now a full format will start which remove write protection from USB Memory Stick.
Always use the Safely Remove Hardware option when taking your flash drive out of the USB port.This will help prevent data loss and corruption of your flash drive.