Fedora xen - Oct 2007 - domU fail to start with error Error: Device 0 (vif) could not be connected. /etc/xen/scripts/vif-route

We have recently upgraded our dom0 to fedora 7 and it was working fine from
last couple of days, today on of domU crashed and when i tries to start it
fails at error ...

xm create -c /etc/xen/vm3.cfg

Error: Device 0 (vif) could not be connected. /etc/xen/scripts/vif-route
failed

in end i have rebooted the host (dom0) and all vms started fine. We never
got this sort of problem at FC6.

Any help in this regards will be highly appreciated.

Askar.