Sometimes portable USB devices get errors like the "disk is write protected" The First thing I would recommend checking is a physical lock on that card or USB Pen Drive, sometimes manufactures provide a write protect lock which will be attached to the card. If this is NOT the case then for your USB Flash Drive, than follow the method in this video.
can't find the key StorageDevicePolicies? you have to create it manually.
1. Right-click HKEY_LOCAL_MACHINE\SYSTEM\CurrrentControlSet\Control\ and select New Key.
2. Enter the name StorageDevicePolicies.
3. Click on the new registry key StorageDevicePolicies and on the right pan right-click, select New DWORD and give it the name WriteProtect.
4. Double click on it and set its value to 0.
You won't be able to copy files to drive or format drive.