[libvirt-users] INTERNAL ERROR:can not attach network interface for vm

hello,i got a error message when use virsh attach-interface for a vm: first, list the vm's interface,there's no interface now. virsh # domiflist ubuntum-124 Interface Type Source Model MAC ------------------------------------------------------- then,i did an attach-interface action: virsh # attach-interface ubuntum-124 bridge br0 --persistent Interface attached successfully virsh # domiflist ubuntum-124 Interface Type Source Model MAC ------------------------------------------------------- vnet0 bridge br0 - 52:54:00:3d:d1:ea second,detach the interface: virsh # detach-interface ubuntum-124 bridge Interface detached successfully virsh # domiflist ubuntum-124 Interface Type Source Model MAC ------------------------------------------------------- 3rd,attach interface again,at this step ,i got erros like below: virsh # attach-interface ubuntum-124 bridge br0 --persistent error: Failed to attach interface error: internal error unable to execute QEMU command 'device_add': Duplicate ID 'net0' for device virsh # attach-interface ubuntum-124 bridge br0 error: Failed to attach interface error: internal error unable to execute QEMU command 'device_add': Duplicate ID 'net0' for device virsh # version Compiled against library: libvir 0.9.10 Using library: libvir 0.9.10 Using API: QEMU 0.9.10 Running hypervisor: QEMU 0.12.1 any one can help?thanks.