lb build : "WARNING: The following packages cannot be authenticated!" error

[debmailist@Safe-mail.net]

Yesterday I tried to build Debian Live image but I encountered an error:

    >WARNING: The following packages cannot be authenticated!
    >libuuid-perl linux-base libklibc klibc-utils initramfs-tools linux-image-3.2.0-4-486 linux-image-3.2.0-4-686-pae libc6-i686 busybox firmware linux-free linux-image-486 linux-image-686-pae
    >E: There are problems and -y was used without --force-yes


I tried:
lb clean --purge
and just plain build with default settings:
lb config
lb build
but still the same result
So I tried that on other machine in virtualbox on clean wheezy installation - still the same thing.
I suppose this has something to do with apt and repositories signing keys.
What is going on? How to fix this?