Just today I erased a small (4GB) thumb drive which had some live system on
it, in order to use it for file transfer purposes instead. I could not
copy+paste anything on it because of write protection until I formatted it as
GPT instead of MBR (which is the default option in the Discs utility).
Given the time it took for deep formatting it, I would not try it on a 256GB
drive, but if fast formatting is an option for you, it might solve your
current problem.
I then created a FAT partition on it because the said files will most
probably be transfered to a non-linux OS, but I do not think the partition
format was the problem.
