Can you remove the /home/robru/.machines/clean-precise-i386.qcow2 file, and try again, and then attach the log file generated in /var/log/libvirt/libvirtd.log and whatever is in /var/log/libvirt/qemu?
Can you remove the /home/robru/ .machines/ clean-precise- i386.qcow2 file, and try again, and then attach the log file generated in /var/log/ libvirt/ libvirtd. log and whatever is in /var/log/ libvirt/ qemu?