If the USB drive appears to be write protected check out this possible reasons:

1. See if the USB drive has a small switch for write protection.

2.Go to the registry under HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\StorageDevicePolicies. The value 'WriteProtect' should be absent or set to '0'.

3. Flash memory has a limited lifetime of about 100.000 guaranteed write cycles. Cells that become damaged must be replaced by reserve cells and then all reserve cells are consumed the flash controller rejects all write accesses.