http://d-i.debian.org/daily-images/amd64/daily/ is broken since a few days...
and build_netboot.log ends with:
dpkg: version '1%3a1.17.1-2' has bad syntax: invalid character in version number
Needed busybox-udeb not found (looked in apt.udeb/cache/archives/, debugudebs/)
make: *** [stamps/get_udebs-netboot-stamp] Error 1
make: *** [_build] Error 2
make: *** [build_netboot] Error 2