Comment 4 for bug 1491725

from cobbler log:
Wed Sep 2 15:17:31 2015 - INFO | Exception occured: <class 'cobbler.cexceptions.CX'>
Wed Sep 2 15:17:31 2015 - INFO | Exception value: 'MAC address duplicated: 0c:c4:7a:14:25:36'
Wed Sep 2 15:17:31 2015 - INFO | Exception Info:
  File "/usr/lib/python2.6/site-packages/cobbler/remote.py", line 2058, in _dispatch
    return method_handle(*params)
   File "/usr/lib/python2.6/site-packages/cobbler/remote.py", line 838, in modify_system
    return self.modify_item("system",object_id,attribute,arg,token)
   File "/usr/lib/python2.6/site-packages/cobbler/remote.py", line 831, in modify_item
    return method(arg)
   File "/usr/lib/python2.6/site-packages/cobbler/item_system.py", line 695, in modify_interface
    if field == "macaddress" : self.set_mac_address(value, interface)
   File "/usr/lib/python2.6/site-packages/cobbler/item_system.py", line 384, in set_mac_address
    raise CX("MAC address duplicated: %s" % address)