Comment 9 for bug 1273925

I'm still having the issue too with usb-creator-gtk 0.2.56.1

Here is a workaround :

1 Open unity dash
2 Search for "Disks" and open the software
3 Select your usb stick in the peripherals list
4 Click the little gears then select "Restaure disk image"
5 "Restaure" Ubuntu iso image onto your stick

And... voilà! Here is your bootable usb stick.