What does the error pool/restricted:E: Tree walking failed - ftw (2: No such file or directory) mean?

Question

linux

Actually, I’m trying this article to try to make my Bolgenos assembly (put additional packages into it), well, only I have everywhere instead of hardy, 8.04 and i386, respectively, trusty, 14.04 and amd64
I get to this piece:

BUILD=/opt/cd-image
APTCONF=/opt/apt-ftparchive/release.conf
DISTNAME=hardy

pushd $BUILD
apt-ftparchive -c $APTCONF generate /opt/apt-ftparchive/apt-ftparchive-deb.conf
apt-ftparchive -c $APTCONF generate /opt/apt-ftparchive/apt-ftparchive-udeb.conf
apt-ftparchive -c $APTCONF generate /opt/apt-ftparchive/apt-ftparchive-extras.conf
apt-ftparchive -c $APTCONF release $BUILD/dists/$DISTNAME > $BUILD/dists/$DISTNAME/Release

gpg --default-key "YOURKEYID" --output $BUILD/dists/$DISTNAME/Release.gpg -ba $BUILD/dists/$DISTNAME/Release
find . -type f -print0 | xargs -0 md5sum > md5sum.txt pool/restricted:E: Tree walking failed - ftw (2: Нет такого файла или каталога
popd

And then the gag happens, apt-ftparchive -c $APTCONF generate /opt/apt-ftparchive/apt-ftparchive-deb.conf gives the error pool/restricted:E: Tree walking failed - ftw (2: No such file or directory)
What the saddest thing is that I can not google any similar cases.