Try opening up a Administrative command prompt and then type each line and hit enter.
Diskpart
List disk (find your pen drive and note its disk #
Select Disk # (from above)
Clean
If it still gives you the error, destroy it and toss it.
Contrary to what Mr. Corcoran said up there, I have drives do this to me every once in a while from Kingston and I have hundreds of them, all the exact same model. Sometimes it just happens. Sometimes the above works, some times it does not.