Comment 11 for bug 722019

I had the problem and my workaround was to run usb-creator-gtk as a regular user (i.e.: not as root) and also by slowly take my time to enter my password when usb-creator-gtk is trying to install the bootloader.

My best guess as the why: I believe the partition table is set to be re-read just before installing the bootloader and since a USB device can sometimes take a while to disappear/reappear the application is just trying too fast to install the bootloader.

There could be something also with the FTL layer being busy as hell with the copying/unmount/sync that just happened. (FTL being an important component in the USB key's firmware)