[live-build] /casper/vmlinux:file not found

[leyoy@free.fr]

Good morning,

I'm trying to build an ubuntu live.
Here's my config file:

lb config noauto \
--architecture amd64 \
--mode="ubuntu" \
--initramfs="casper" \
--distribution="precise" \
--archive-area="main multiverse restricted universe" \
--mirror-bootstrap="http://fr.archive.ubuntu.com/ubuntu/"; \
--mirror-chroot-security="http://security.ubuntu.com/ubuntu/"; \
--mirror-binary="http://fr.archive.ubuntu.com/ubuntu/"; \
--mirror-binary-security="http://security.ubuntu.com/ubuntu/"; \
--bootappend-live="locales=fr_FR.UTF-8 keyboard-layouts=fr timezone=Europe/Paris" \
"${@}"

the building seems to be ok but when i try my usb stick I have the message:
/casper/vmlinux:file not found :(
is there some issues ?

Thank you for your help