Startup Disk Creator shows no free space on my USB stick

Actually, there is another way to create bootable USB drive with the "Disks" utility. All you need to do is "restore disk image" using the iso file as the source image and you're good to go.

If you need more help...

1. Open "Disks" utility.
2. Choose the USB drive from the side.
3. Press the little "stop" ( ■ ) button.
4. Delete all file systems with the minus ( - ) button (WARNING: THIS WILL DELETE ALL THE DATA ON THE USB DRIVE!).
5. Press the "two gears" button and select "Restore Disk Image".
6. Under "Image to restore" choose your downloaded iso file.
7. Press "Start Restoring" and you're done.

The whole process should not take more then 10 minutes.
GOOD LUCK :)

Note: some OSs like Windows won't be able to use the USB drive until you format it again.

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/

I saw the same problem. Here is how I solved it:

1. If needed, install the dosfstools

   sudo apt-get install dosfstools

2. Find out which disk needs to be reformatted. This will show a list and one of those in the list will be the USB drive you would like to reformat. In my case it was /dev/sdb1.

   fdisk -l

3. Reformat the USB drive with something like this (NOTE: THIS WILL DELETE ALL DATA ON THE DRIVE)

   mkdosfs -F 32 -I /dev/sdb1

Also you may have to unmount the usb drive first with the following:

 `umount /dev/sdb1'

You should now be able to return to the Startup Disk Creator and build the Ubuntu boot drive.