Startup Disk Creator error [closed]

I get this error when trying to "Erase Disk" on Startup Disk Creator.

^{(Click image to enlarge)}

org.freedesktop.DBus.Python.AttributeError: 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 250, in Format
    partition = table.call_create_partition_sync(0, size, '0x0c', '', no_options, None)
AttributeError: 'NoneType' object has no attribute 'call_create_partition_sync'

Look at the color differences in the Make Startup Disk window. Everything below the "Erase Disk" button / "Disk to use" section is gray (buttons plus slider are disabled, so I can't change either of them).

1. What is this error message trying to say me?

2. What should I do to get rid of this error/problem? I need clear detailed instructions because I'm a newbie to the Ubuntu world!

The Startup Disk Creator tool is known to having some issues.
Use the Disks tool to create the Ubuntu installation media properly.

Open Disks, select Restore Disk Image from the menu on the top right of the application.
Choose the Ubuntu installation ISO file and the USB drive to write it to - then start restoring.