The reason that usb-creator-gtk doesn't work may be because the iso file is not on a local file system.
When I selected an iso file on an sshfs mounted filesystem, it refused to create the disk, displaying an error message indicating "Installation failed". Once I moved the .iso file to the local file system it worked without any issues.
This is on xubuntu 13.10
Interesting! It is worth looking into this problem. What OS (version and flavour of Ubuntu) were you running?