Edit the scripts variable to be /dev/loop0 Code: LOOPBACK_DEVICE=/dev/loop0 That is not needed, this output is normal as script tries to unmount temprorary loopback device when started. Seems he has problem with 7z archiver. SSLMM, are you able to run 7z from the command line?
LOOPBACK_DEVICE=/dev/loop0
apt-cache policy p7zip-full