Are you erasing the volume or the drive?
This happens to me every time I try to reformat an external drive on Sierra. The first time I do it, it fails... but if I then do it again, it usually works!
So... maybe try it again?
erasing all External Storage
i'm already trying but i think the storage is damaged
Could be damaged but as has been mentioned the damn thing fails every time here sometimes three or four tries are needed with that new steaming pile of dung that have put out.
i can erasing by terminal