Hey there, M o O N.
Try the drive with a different computer to see if the issue still persists. You should also try the suggestions from this article: http://www.wikihow.com/Disable-Write-Protection. If neither of those tips is useful, you could try download the USB flash drive manufacturer's format tool, to try and reformat it, to see if that fixes things up (not that you'll lose the data from the pen drive by following this method).
If you're still unable to do anything about the write protection of the flash drive, then it might have failed. If this is the case, I'd advise you to try to RMA it, as long as it's still under warranty.
Hope that helps. Please let me know how everything goes.
Boogieman_WD