Comment 1 for bug 111227

did you set the right options to create a netboot initramfs in /etc/initramfs-tools/initramfs.conf and updated the initramfs with update-initramfs -u ?

nfs root works fine for plenty ltsp users in feisty and it seems it also worked flawlessly when the netbooting installer images were tested (according to https://www.stgraber.org/ubuntu/isotesting/test/173)