You should not run unetbootin as root user; instead log in as a non-root user and run the following command:
# or try su with a dash:
su username -c "dbus-launch --exit-with-session unetbootin"
Due to recent security changes in Fedora and other distributions, root users cannot provide applications with dbus connections, therefore neither session management nor gio functionality are available, which is needed for unetbootin to work. In any case, this is the behavior of the operating system which we cannot change. See http://forums.fedoraforum.org/showthread.php?p=1420900 for details.