Comment 4 for bug 816464

Here is the error I get from virt-manager 0.9 gui every time I try to select 'Virtio'. Selecting 'Default' or 'IDE' does not display any error. After this error the virtio setting is reverted.

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[Sun, 29 Jan 2012 13:26:08 virt-manager 2536] DEBUG (error:80) dialog message: Error changing VM con
figuration: 'NoneType' object has no attribute 'xpathEval' : Error changing VM configuration: 'NoneT
ype' object has no attribute 'xpathEval'

Traceback (most recent call last):
  File "/usr/share/virt-manager/virtManager/details.py", line 2317, in _change_config_helper
    func(*args)
  File "/usr/share/virt-manager/virtManager/domain.py", line 574, in define_disk_bus
    return self._redefine_device(change, devobj)
  File "/usr/share/virt-manager/virtManager/domain.py", line 307, in _redefine_device
    return cb(dev)
  File "/usr/share/virt-manager/virtManager/domain.py", line 570, in change
    editdev.address.clear()
  File "/usr/lib/pymodules/python2.7/virtinst/VirtualDevice.py", line 173, in clear
    self._remove_child_xpath("./address")
  File "/usr/lib/pymodules/python2.7/virtinst/XMLBuilderDomain.py", line 458, in _remove_child_xpath
    _remove_xpath_node(self._xml_ctx, xpath, dofree=False)
  File "/usr/lib/pymodules/python2.7/virtinst/XMLBuilderDomain.py", line 186, in _remove_xpath_node
    node = _get_xpath_node(ctx, curxpath)
  File "/usr/lib/pymodules/python2.7/virtinst/XMLBuilderDomain.py", line 71, in _get_xpath_node
    node = ctx.xpathEval(xpath)
AttributeError: 'NoneType' object has no attribute 'xpathEval'