求助：live debian制作： lb build的错误信息怎么回事？

sd02

输出信息如下：
debian-archive-keyring is already the newest version.
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Hit http://ftp.de.debian.org squeeze Release.gpg                              
Ign http://ftp.de.debian.org/debian/ squeeze/main Translation-en
Hit http://ftp.de.debian.org squeeze-updates Release.gpg
Hit http://security.debian.org squeeze/updates Release.gpg
Ign http://security.debian.org/ squeeze/updates/main Translation-en
Ign http://ftp.de.debian.org/debian/ squeeze-updates/main Translation-en
Hit http://ftp.de.debian.org squeeze Release
Hit http://security.debian.org squeeze/updates Release               
Hit http://ftp.de.debian.org squeeze-updates Release
Hit http://security.debian.org squeeze/updates/main amd64 Packages   
Hit http://ftp.de.debian.org squeeze/main amd64 Packages
Get:1 http://ftp.de.debian.org squeeze-updates/main amd64 Packages/DiffIndex [2023 B]
Hit http://ftp.de.debian.org squeeze-updates/main amd64 Packages
Fetched 2023 B in 3s (573 B/s)
Reading package lists... Done
Reading package lists... Done
Building dependency tree      
Reading state information... Done
P: Begin building root filesystem image...
P: Preparing squashfs image...
P: This may take a while.
Cannot stat source directory "chroot" because No such file or directory
P: Begin unmounting filesystems...
请教哪位高人对live debian熟悉的，怎么解决？
没有什么特殊配置，前面只是用了lb config -b usb-hdd