Thanks for taking time to report this bug and help make ubuntu better. Can you please open gpared (if not already installed install it with sudo apt-get install gparted) and then format you thumb drive into fat32 with it, remove you thumb drive and insert it again and try again.
Thanks for taking time to report this bug and help make ubuntu better. Can you please open gpared (if not already installed install it with sudo apt-get install gparted) and then format you thumb drive into fat32 with it, remove you thumb drive and insert it again and try again.