Xen + libvirt - Domains not found

I have installed a VM with Xen Hypervisor (xl commands) , but when I try to view the information about the VM through the libvirt (lookupByName/lookupByID), I have the following error:

libvirt: Xen Light Driver error : Domain not found
Traceback (most recent call last):
File "lookupByID.py", line 11, in <module>
dom = conn.lookupByID(domainID)
File "/usr/lib/python2.7/dist-packages/libvirt.py", line 3867, in lookupByID
if ret is None:raise libvirtError('virDomainLookupByID() failed', conn=self)
libvirt.libvirtError: Domain not found