I am using the latest scripts from experimental 4.0~alpha31-1 and am using a sid build environment.
Despite the message (see below), this file does exist.
#!/bin/sh
set -e
lb config noauto \
--apt-recommends false \
--apt-options "--yes --no-install-recommends" \
--apt-secure true \
--apt-indices false \
--distribution "sid" \
--archive-areas "main contrib non-free" \
--architecture "amd64" \
--linux-flavours "amd64" \
--debian-installer live \
--debian-installer-distribution daily \
--memtest none \
--security false \
--updates false \
--debug \
--verbose \
--win32-loader false
[2014-01-17 06:15:05] lb build noauto
P: live-build 4.0~alpha31
P: Building config tree for a debian/sid/amd64 system
[2014-01-17 06:15:05] lb bootstrap
P: Setting up cleanup function
[2014-01-17 06:15:05] lb bootstrap-debootstrap
I: Retrieving Release
I: Retrieving Release.gpg
I: Checking Release signature
E: Invalid Release signature (key id 8B48AD6246925553)
cp: cannot create directory ‘cache/bootstrap’: No such file or directory
[2014-01-17 06:15:08] lb chroot_devpts install
P: Begin mounting /dev/pts...
[2014-01-17 06:15:08] lb chroot_proc install
P: Begin mounting /proc...
[2014-01-17 06:15:09] lb chroot_selinuxfs install
[2014-01-17 06:15:09] lb chroot_sysfs install
P: Begin mounting /sys...
[2014-01-17 06:15:09] lb chroot_debianchroot install
P: Configuring file /etc/debian_chroot
/usr/lib/live/build/chroot_debianchroot: 50: /usr/lib/live/build/chroot_debianchroot: cannot create chroot/etc/debian_chroot: Directory nonexistent
P: Begin unmounting filesystems...
P: Saving caches...
chroot: failed to run command ‘/usr/bin/env’: No such file or directory