Thanks for the log. You do not install any kernel package inside the nfsroot. I guess it's because of the ubuntu version of FAI on your host system.
The main problem may be inside /etc/fai/NFSROOT or in fai-make-nfsroot itself. IIRC we made some changes there. Can you please try to upgrade your fai packages on the host. Have a look at https://launchpad.net/~fai/+archive/ubuntu/ppa. Please send the /etc/fai/NFSROOT so I can check this file. -- regards Thomas