What model drive is this?
Some have a write protect switch that allows for you to enable/disable write protection. If this drive was one that you got for free with demo software etc on it or one that came from a computer manufacturer with system recovery software on it, then it may be a 1 time write device.
I have seen people get the USB sticks at conventions with no intent to use the info that is on them, they then get home and try to format the flash stick and to their surprise it can not be formatted and files cant be deleted from it.
If its a flash stick that all of a sudden write protected itself and its not one with write protection switch feature, then the stick is likely damaged and I would copy the data off of it to hard drive etc since it still may read fine, but unable to write to this device because of a failure.
