Constructing of filelist failed: error - index error

I’m trying to backup a Linux machine running Slackware64 14.2.
It’s a VirtualBox VM with a single virtual hard disk. On the disk there’s a single LVM volume, with 2 logical volumes (boot and /).

When I backup /etc and /root, all is ok.
If I add /home to the backup list, I always get the error “Constructing of filelist of “darkstar” failed: error - index error” (where “darkstar” is the hostname of the VM).

Can someone help me understand what’s happening?