I set virt-manager in qemu:///system space and tried to add new VM but it didn't proceed. I figured out its duo to serial numbers is in cryptic form.

# cat /sys/devices/virtual/dmi/id/product_serial
ÿÿÿÿÿÿÿ


#virt-manager --debug
Traceback (most recent call last):
  File "/usr/share/virt-manager/virtManager/libvirtobject.py", line 225, in _reparse_xml
    self._xmlobj = self._build_xmlobj(self._get_raw_xml())
  File "/usr/share/virt-manager/virtManager/libvirtobject.py", line 228, in _build_xmlobj
    return self._parseclass(self.conn.get_backend(), parsexml=xml)
  File "/usr/share/virt-manager/virtManager/nodedev.py", line 27, in _parse_convert
    return NodeDevice.parse(conn, parsexml)
  File "/usr/share/virt-manager/virtinst/nodedev.py", line 95, in parse
    tmpdev = NodeDevice(conn, parsexml=xml, allow_node_instantiate=True)
  File "/usr/share/virt-manager/virtinst/nodedev.py", line 106, in __init__
    XMLBuilder.__init__(self, *args, **kwargs)
  File "/usr/share/virt-manager/virtinst/xmlbuilder.py", line 777, in __init__
    parent_xpath, relative_object_xpath)
  File "/usr/share/virt-manager/virtinst/xmlbuilder.py", line 679, in __init__
    self._parse(parsexml, parsexmlnode)
  File "/usr/share/virt-manager/virtinst/xmlbuilder.py", line 692, in _parse
    doc = libxml2.parseDoc(xml)
  File "/usr/lib/python2.7/site-packages/libxml2.py", line 1327, in parseDoc
    if ret is None:raise parserError('xmlParseDoc() failed')
libxml2.parserError: xmlParseDoc() failed
[Sun, 12 Apr 2015 06:06:16 virt-manager 4241] DEBUG (create:165) Showing new vm wizard
[Sun, 12 Apr 2015 06:06:16 virt-manager 4241] DEBUG (create:892) Guest type set to os_type=hvm, arch=x86_64, dom_type=kvm
[Sun, 12 Apr 2015 06:06:16 virt-manager 4241] DEBUG (xmlbuilder:694) Error parsing xml=
<device>
  <name>computer</name>
  <capability type='system'>
    <product>Vostro</product>
    <hardware>
      <vendor>Dell Inc.</vendor>
      <version>A10</version>
      <serial>ÿÿÿÿÿÿÿ</serial>
      <uuid>REMOVED</uuid>
    </hardware>
    <firmware>
      <vendor>Dell Inc.</vendor>
      <version>A10</version>
      <release_date>05/18/2013</release_date>
    </firmware>
  </capability>
</device>

[Sun, 12 Apr 2015 06:06:16 virt-manager 4241] ERROR (create:346) Error setting create wizard conn state.
Traceback (most recent call last):
  File "/usr/share/virt-manager/virtManager/create.py", line 344, in reset_state
    self.set_conn(activeconn, force_validate=True)
  File "/usr/share/virt-manager/virtManager/create.py", line 225, in set_conn
    self.set_conn_state()
  File "/usr/share/virt-manager/virtManager/create.py", line 626, in set_conn_state
    self.netlist.reset_state()
  File "/usr/share/virt-manager/virtManager/netlist.py", line 405, in reset_state
    self._populate_network_list()
  File "/usr/share/virt-manager/virtManager/netlist.py", line 253, in _populate_network_list
    vnet_bridges)
  File "/usr/share/virt-manager/virtManager/netlist.py", line 185, in _find_physical_devices
    for nodedev in self.conn.get_nodedevs("net"):
  File "/usr/share/virt-manager/virtManager/connection.py", line 648, in get_nodedevs
    xmlobj = dev.get_xmlobj()
  File "/usr/share/virt-manager/virtManager/libvirtobject.py", line 160, in get_xmlobj
    self._reparse_xml()
  File "/usr/share/virt-manager/virtManager/libvirtobject.py", line 225, in _reparse_xml
    self._xmlobj = self._build_xmlobj(self._get_raw_xml())
  File "/usr/share/virt-manager/virtManager/libvirtobject.py", line 228, in _build_xmlobj
    return self._parseclass(self.conn.get_backend(), parsexml=xml)
  File "/usr/share/virt-manager/virtManager/nodedev.py", line 27, in _parse_convert
    return NodeDevice.parse(conn, parsexml)
  File "/usr/share/virt-manager/virtinst/nodedev.py", line 95, in parse
    tmpdev = NodeDevice(conn, parsexml=xml, allow_node_instantiate=True)
  File "/usr/share/virt-manager/virtinst/nodedev.py", line 106, in __init__
    XMLBuilder.__init__(self, *args, **kwargs)
  File "/usr/share/virt-manager/virtinst/xmlbuilder.py", line 777, in __init__
    parent_xpath, relative_object_xpath)
  File "/usr/share/virt-manager/virtinst/xmlbuilder.py", line 679, in __init__
    self._parse(parsexml, parsexmlnode)
  File "/usr/share/virt-manager/virtinst/xmlbuilder.py", line 692, in _parse
    doc = libxml2.parseDoc(xml)
  File "/usr/lib/python2.7/site-packages/libxml2.py", line 1327, in parseDoc
    if ret is None:raise parserError('xmlParseDoc() failed')
parserError: xmlParseDoc() failed


Regards
Roz