I snipped the first 5 megs:
dd if=ngc-multi-001.gcm of=ngc-multi-001.gcm.5m bs=1024 count=5120
and it has been emailed to support atthesiteof img burn dotdot com. (I'm sure you're already getting spam to that email, but maybe this won't make it worse).
Thanks for being willing to look at it. For all I know the utility that creates this ISO may be doing something "wrong."
Bromius