The Ubuntu start-up disk creator has proved, for me at least, very flaky.
Consequently, I always use the Mint version, which includes a usb formatter as well as writer.
This is where I get it from:
sudo add-apt-repository ppa:tsvetko.tsvetkov/trusty-backports
sudo apt-get update
sudo apt-get install mintstick
I haven’t tested it in later versions of UM and so cannot confirm it works in them.
I tried it Steve and it seems to be hit & miss as to whether it succeeds in creating a bootable image!. 
I have tried other tools and it seems that nearly if not all; are broken at the moment?. 
Hi Wolfman. I am using 14.04 at the moment and it works well. So, I wonder if it is something that has changed in the OS in terms of its compatibility with these tools post 14.04?
You might be right there Steve, I haven’t tried it on 14.04 and am using 15.10 and 16.04 Alpha!.