Description of problem: Somehow during the gdm update to gdm-2.14.1-1.fc5.2 my /etc/gdm/custom.conf got deleted. Running gdmsetup in that case causes a crash of gdmsetup when trying to set security login settings. Workaround copy /etc/gdm/custom.conf.rpmsave to /etc/gdm/custom.conf and gdmsetup works again.
Same problem here after upgrading from FC4
Actually, after poking around, my problem seems to be worse. I still have /etc/gdm/custom.conf, yet for some reason, gdmsetup is bombing out complaining "Could not access GDM configuration file."
the upgrade logic for gdm has been reworked a few times since this report. I'm going to close, but if you end up with any more problems feel free to reopen.