Start by googling "nautilus-GDU". From what it shows, I'd say your best source of information woulf be the Fedora forums and knowledge base.
From the description I read, it sounds like the device you're trying to format is not a supported device. Are you sure you have the correct device name (i.e. /dev/sdb1). Are you able to mount the device as user and not root? If not, you might need to add yourself to the "cdrom" group or add the cdrom to fstab with user privilege (/dev/sr0 /media iso9660 user,noauto,suid,rw 0 0)
I assume with Nautilus you're using gnome which I'm not familiar with so can't suggest much else.
Tom (retired penguin)