Comment 9 for bug 1342633

Posible Solution:

I have replaced the following files in the cobbler docker path: /var/lib/tftpboot/images/ubuntu_1204_x86_64
initrd.img
linux

With the image pulled from the 5.0 repo, it appears that the boot images in the 5.1 repo are corrupt.
http://fuel-repository.mirantis.com/fwm/5.0/ubuntu/installer-amd64/current/images/netboot/ubuntu-installer/amd64/