when gparted is started from the menu via gksu-polkit the path is set to /usr/local/bin:/bin:/usr/bin ntfsprogs for example used by gparted are in /usr/sbin to be able to detect the the PATH needs to include at least /usr/sbin i don't know where this should be fixed. ideally a policy file for gparted would be created which sets the PATH (is that possible? running gksu-polkit xterm; gives a different path, so there must be something setting that). alternatively a workaround would be to manually fix the PATH in the /usr/bin/gparted script