Here are some instruction :
-Run Registry Editor (regedit).
-Navigate to the following registry key: -HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control
-Create a New Key named as StorageDevicePolicies.
-Highlight StorageDevicePolicies, and then create a New DWORD (32-bit) Value named as WriteProtect.
-Double click on WriteProtect, and set its value data to 1.
To read more about this try looking here : http://www.techyv.com/questions/how-remove-write-protection-flash-drive