Fails on the `qvm-start HVM_tails-3_3 --cdrom=untrusted1:/home/user/Downloads/tails.iso` step in the https://www.qubes-os.org/doc/tails/ write up.
The <source dev="{{ device.device_node }}" /> throws the error.
This comes from a vm.devices.block.assignments(True) call in xen.xml.
I have the same exact issue but with win7