There are three possibilities, in my opinion:
1. Your ISO is corrupt and not bootable. Since the MDMSUM has not been released officially for these unofficial leaks there is no way to know reliably if this is a corrupt or fake ISO. But you could compare a working ISO of the same build to determine if the # of bytes or MDMSUM is the same.
2. (More likely) Your DVDRW may not be able to either write bootable images or read bootable images. It could be a physical problem with the device. Try to burn a different bootable image that should work and see if that solves it.
3. Try a different program besides UltraISO (MagicISO/MagicDisc comes to mind).
I can think of no other causes off hand.