boot - Startup Disk Creator shows no free space on my USB stick

I am having a problem trying to use Startup Disk Creator with my 8GB USB stick. The USB stick has just been formatted, but Startup Disk Creator shows that there is no free space on the drive, although I can use it just fine. I am not sure whether the problem comes from when I used the drive previously with Windows 7 USB DVD Download Tool to install Windows on another computer? When I press 'Erase Disk', it shows the message below:

org.freedesktop.DBus.Python.gi._glib.GError: Traceback (most recent call last):

  File "/usr/lib/python3/dist-packages/dbus/service.py", line 707, in _message_cb
    retval = candidate_method(self, *args, **keywords)
  File "/usr/share/usb-creator/usb-creator-helper", line 239, in Format
    block.call_format_sync('dos', GLib.Variant('a{sv}', {'erase': GLib.Variant('s', '')}), None)
gi._glib.GError: GDBus.Error:org.freedesktop.UDisks2.Error.Failed: Error synchronizing after initial wipe: Timed out waiting for object

You can try to erase/format disk with: 1. Gparted or 2. Disk Utility

sudo apt-get install gparted


sudo apt-get install gnome-disk-utility

UPDATE:
You will probably need to unmount all partition(s) in Gparted (or in Disk Utility) and then delete them all and create one. Also you can do a startup disk in Unetbootin http://unetbootin.sourceforge.net/