usb-creator won't create startup disk

I'm running usb-creator-gtk 0.2.23 on Ubuntu 12.04, x86_64.

I'm trying to create a bootable USB stick (7.5G) for Ubuntu 12.04 (x86_64) from another Ubuntu 12.04 x86_64 PC.

I downloaded the Ubuntu 12.04 LTS "Precise Pangolin" - Release amd64 (20120425).

When I run Make Startup Disk, I selected the downloaded release. The drive shows up with a capacity of 7.5GB and a blank space under "Free Space". I have tried using the "Erase Disk" button, which seems to erase the disk.

The problem is that the options below the "Disk to use" section are grayed out. The "Make Startup Disk" is colored dull orange, while the source disc image and device to use are bright orange. The "Make Startup Disk" button doesn't do anything when I click it. The only working buttons are "Other...", "Erase Disk", and "Close".

Upon using Other button to select the ISO, it allows to select the ISO but it doesn't load and the "Source Disk Image" field remains empty.