VM fails to spawn

Hello,

I'm trying to run an Openstack Compute on OVM 3.3.1 with Xen but when I try to launch a VM it return me an error.

An error occurred while trying to launch a defined domain with xml: <domain type='xen'>

  <name>instance-00000048</name>

  <uuid>50c0057f-cf3a-4dd7-8e2a-341731cffed5</uuid>

  <memory unit='KiB'>524288</memory>

  <currentMemory unit='KiB'>524288</currentMemory>

  <vcpu placement='static'>1</vcpu>

  <bootloader></bootloader>

  <os>

    <type>linux</type>

  </os>

  <clock offset='utc' adjustment='reset'/>

  <on_poweroff>destroy</on_poweroff>

  <on_reboot>restart</on_reboot>

  <on_crash>destroy</on_crash>

  <devices>

    <emulator>/usr/lib/xen/bin/qemu-dm</emulator>