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 237, in Format
    part.call_set_type_sync('0x0c', no_options, None)
gi._glib.GError: GDBus.Error:org.freedesktop.UDisks2.Error.Failed: Error setting partition flags on /dev/sdb2: Command-line `sfdisk --change-id "/dev/sdb" 2 0x0c' exited with non-zero exit status 1:
WARNING: GPT (GUID Partition Table) detected on '/dev/sdb'! The util sfdisk doesn't support GPT. Use GNU Parted.

Use the --force flag to overrule this check.

exec sudo -i
dd if=/home/user/Downloads/ubuntu-16.04.1-desktop-amd64.iso of=/dev/sdb
           <path to .iso>                                   <USB stick>