The main reason for this problem, it seems, is a virus.
Try this first: In my Computer. right click on that drive's letter> Properties> Security>Change the permissions for Write to Allow.
Some people were able to regain access to their USB drive via a Register Edit
1. Open Start Menu >> Run, type regedit and press Enter, this will open the registry editor.
2. Navigate to the following path:
Note: If the registry key StorageDevicePolicies key does not exist, you will need to create it
Download this batch file called add.bat, and double click after download the key will be automatically added to registry.http://www.troublefixers.com/wp-co
3. Double click the key WriteProtect in the right pane and set the value to 0 in the Value Data Box and press OK button
4. Exit Registry, restart your computer and then again re-connect your USB pen drive on your computer. That is it, done.
Others were able to format their Drive using this utility. However it will erase your data, so back it up first.http://www.box.net/shared/9hgp81ndgs