Can't boot. syslinux ERROR: No configuration file found

[Chris <bbshliu@gmail.com>]

Hi,

I built a live system with the latest live-build package(Version: 3.0~a13-1). But when I test it with qemu, I got the error message:

SYSLINUX 4.03 20110219 ...
ERROR: No configuration file found
No DEFAULT or UI configuration directive found!
boot:

After writing the img to my usb drive, I got the same error.

Then I tried to build a minimal system, but still didn't work.
My auto/config file is as follow:

#!/bin/sh


lb config noauto \
    --distribution wheezy \
    --binary-filesystem fat32 \
    --volatile false \
    -b usb-hdd --username chris --apt aptitude \
    --parent-mirror-bootstrap http://mirror.dlut.edu.cn/debian \
    --parent-mirror-chroot http://mirror.dlut.edu.cn/debian \
    --parent-mirror-chroot-security http://mirror.dlut.edu.cn/debian-security \
    --parent-mirror-binary http://mirror.dlut.edu.cn/debian \
    --parent-mirror-binary-security http://mirror.dlut.edu.cn/debian-security \
    --mirror-bootstrap http://mirror.dlut.edu.cn/debian \
    --mirror-chroot http://mirror.dlut.edu.cn/debian \
    --mirror-chroot-security http://mirror.dlut.edu.cn/debian-security \
    --mirror-binary http://mirror.dlut.edu.cn/debian \
    --mirror-binary-security http://mirror.dlut.edu.cn/debian-security \
    "${@}"

I also tried the fat16 file system. It didn't work.
BTW, I successfully built the system several days ago.
Could anyone give me some suggestions?