Sometimes, your pen drive goes write-protected all of a sudden.
In this situation, you can not delete or write anything on the flash drive. You cannot even format your own flash drive.
This might happen because of virus, hardware switch or some other reason.
Another fact out of my experience is that hoping to solve the problem with linux distro will not help. The problem persists on every OS.
makeuseof has given it a good shot.
First try those steps on the makeuseof blog, but if they do not work, don't be upset because i have a couple of more ideas to try.
1. Look for the recovery tools provided by the manufacturer of the flash drive
eg. Transcend : http://in.transcend-info.com/Support/Software-3/ (it worked for me)
2. If it is covered in warranty, return/replace it.
3. Try mUsbFixer from http://musbfixer.in/
Tried on : Transcend flash drive 8GB
May work with : other flash drives