500 error: UnboundLocalError: local variable 'key_required' referenced before assignment

It doesn't look like it can be a duplicate of bug 1453954… can you please provide the maas logs (/var/log/maas/*) from around the time the error happened so that we can identify the issue? (You'll find a stacktrace with the "'key_required' referenced before assignment" error).

Here's the "key_required" error message from regiond.log. Please see the regiond and maas attached. The timestamp for this pipeline is around Fri, 08 May 2015 09:39:21.

2015-05-08 09:47:40 [maasserver] ERROR: ################################ Exception: local variable 'key_required' referenced before assignment ################################
2015-05-08 09:47:40 [maasserver] ERROR: Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/django/core/handlers/base.py", line 112, in get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/usr/lib/python2.7/dist-packages/maasserver/api/support.py", line 52, in __call__
    response = upcall(request, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/django/views/decorators/vary.py", line 19, in inner_func
    response = func(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/piston/resource.py", line 167, in __call__
    result = self.error_handler(e, request, meth, em_format)
  File "/usr/lib/python2.7/dist-packages/piston/resource.py", line 165, in __call__
    result = meth(request, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/maasserver/api/support.py", line 200, in dispatch
    return function(self, request, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/maasserver/api/nodes.py", line 401, in start
    form = Form(instance=node)
  File "/usr/lib/python2.7/dist-packages/maasserver/forms.py", line 750, in __init__
    data=data, instance=instance, **kwargs)
  File "/usr/lib/python2.7/dist-packages/maasserver/forms.py", line 410, in __init__
    self.set_up_osystem_and_distro_series_fields(instance)
  File "/usr/lib/python2.7/dist-packages/maasserver/forms.py", line 480, in set_up_osystem_and_distro_series_fields
    initial_value = get_distro_series_initial(osystems, instance)
  File "/usr/lib/python2.7/dist-packages/maasserver/utils/osystems.py", line 157, in get_distro_series_initial
    return '%s/%s%s' % (osystem_name, series, key_required)
UnboundLocalError: local variable 'key_required' referenced before assignment