'rhn-profile-sync' or 'rhnreg_ks' commands gives error "libvirt.libvirtError: no connection driver available"

Issue

• Updating a client profile or registering a client gives error "libvir: error : no connection driver available"

• rhn-profile-sync:

> Updating package profile...  
> Updating hardware profile...  
> Updating virtualization profile...  
> libvir: error : no connection driver available  
> Warning: Could not retrieve virtualization information!  
>         libvirtd service needs to be running.

• rhnreg_ks:

rhnreg_ks --username <RHN or Satellite username> --password <password> --force 

libvir: error : no connection driver available An error has occurred:

libvirt.libvirtError

See /var/log/up2date for more information:

File "/usr/sbin/rhnreg_ks", line 227, in ?

    cli.run()

  File "/usr/share/rhn/up2date_client/rhncli.py", line 66, in run

    sys.exit(self.main() or 0)

  File "/usr/sbin/rhnreg_ks", line 178, in main

    rhnreg.sendVirtInfo(systemId)

  File "/usr/share/rhn/up2date_client/rhnreg.py", line 674, in sendVirtInfo

    support.refresh()

  File "/usr/share/rhn/virtualization/support.py", line 51, in refresh

    if _is_host_domain():

  File "/usr/share/rhn/virtualization/support.py", line 161, in _is_host_domain

    conn = libvirt.open(None)

  File "/usr/lib/python2.4/site-packages/libvirt.py", line 169, in open

    if ret is None:raise libvirtError('virConnectOpen() failed')

libvirt.libvirtError: no connection driver available