It sure would be nice if someone who knows what they are doing took a look at this problem:
https://bugzilla.redhat.com/show_bug.cgi?id=1135762

The current situation on Fedora 21 is that virt-sandbox and virt-sandbox-service simply do not work if a network is defined (e.g., -N address-192.168.1.1/34).  I would give dhcp as an example but to work, that needs to patch I submitted in another BZ report.

Since both virt-sandbox  -c  lxc:///  -N  <network>,source=default and doing systemctl start <sandbox> result in the same error and  since I am running the fedora-virt-preview rpms and the failure does not occur on Fedora 20 but does occur on Fedora 21, I have to assume that the problem is not directly in libvirt.  However, determining what/where the problem really is, is stretching my abilities a bit too far ... help!!