libvirt users - Jun 2012 - guest fails to start: Error initializing virtio-net-pci

Hi, 
squeeze host, winxp guest.  guest fails to start:

   PCI: devfn 24 not available fpr virtio-net-pci, in use by virtio-blk-pci
   Error initializing virtio-net-pci


xml-File:
=======    <disk type='file' device='disk'>
      <driver name='qemu' type='raw'/>
      <source file='/var/lib/winxp'/>
      <target dev='hda' bus='ide'/>
      <address type='drive' controller='0' bus='0'
unit='0'/>
    </disk>
 this added: 
    <disk type='file' device='disk'>
      <driver name='qemu' type='raw'/>
      <source file='/var/lib/winxp-d'/>
      <target dev='hdb' bus='virtio'/>
      <address type='drive' controller='0' bus='0'
unit='1'/>
    </disk>

root at squeeze64:~# lsmod | grep virt
virtio_balloon          2961  0
virtio_net             10573  0
virtio_blk              4225  0
virtio_pci              5511  0
virtio_ring             3258  1 virtio_pci
virtio                  3309  4 virtio_balloon,virtio_net,virtio_blk,virtio_pci


root at squeeze64:~# dpkg -l  | egrep "kvm|qemu|virt"
ii  etherboot-qemu                       5.4.4-9                       
Bootstrapping for various network adapters (qemu)
ii  gvfs                                 1.6.4-3                       
userspace virtual filesystem - server
ii  kvm                                  1:0.12.5+dfsg-5+squeeze8       dummy
transitional package from kvm to qemu-kvm
ii  libvirt-bin                          0.8.3-5+squeeze2               the
programs for the libvirt library
ii  libvirt0                             0.8.3-5+squeeze2               library
for interfacing with different virtualization
systems
ii  python-libvirt                       0.8.3-5+squeeze2               libvirt
Python bindings
ii  qemu                                 0.12.5+dfsg-3squeeze1          fast
processor emulator
ii  qemu-keymaps                         0.12.5+dfsg-3squeeze1          QEMU
keyboard maps
ii  qemu-kvm                             0.12.5+dfsg-5+squeeze8         Full
virtualization on x86 hardware
ii  qemu-system                          0.12.5+dfsg-3squeeze1          QEMU
full system emulation binaries
ii  qemu-user                            0.12.5+dfsg-3squeeze1          QEMU
user mode emulation binaries
ii  qemu-utils                           0.12.5+dfsg-3squeeze1          QEMU
utilities
ii  virt-manager                         0.8.4-8                        desktop
application for managing virtual machines
ii  virt-viewer                          0.2.1-1                       
Displaying the graphical console of a virtual machine
ii  virtinst                             0.500.3-2                      Programs
to create and clone virtual machines


I sucessfully added a virtio NIC: 

    <interface type='bridge'>
      <mac address='52:54:00:a6:fb:ab'/>
      <source bridge='br0'/>
      <model type='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00'
slot='0x03' function='0x0'/>
    </interface>


an I installed the driver from red hat  "virtio-win-0.1-22.iso". But
adding a virtio
disk fails. 

any ideas?
Ekkard