Some times your USB thumb drive or pen drive my face this weired problem, although the drive seems normal and is being detected by the OS, yet it shows the drive is write protected when you try to put some data on it. It can be because of physical errors in the drive or may be because of just some misconfiguration.

Here are few tips you can follow when you face such situations:

Regedit Method:

-run “regedit” command
-find “HKEY_LOCAL_MACHINE/System/Control/StorageDevicePolicies/
-Double click at “Write Protect”
-Change the value to “0″

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HP Drive Key Boot Utility Method:

Download and Install HP Drive Key Boot Utility : http://snipurl.com/hpbootutil

It should work for most brands of flash drives.

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Also check if your drive has write protect notch some where, toggle it then try to format it again.

I hope this would solve your problem. :)