Subject = panelnd.create_nd_panel_factory(klass_name='Subject', axis_orders
    =['setsize', 'location', 'vfield', 'channels', 'samples'], axis_slices=
    {'location': 'labels', 'vfield': 'items', 'channels': 'major_axis',
    'samples': 'minor_axis'}, slicer=pd.Panel4D, axis_aliases={'ss':
    'setsize', 'loc': 'labels', 'vf': 'items', 'major': 'major_axis',
    'minor': 'minor_axis'})
subjects = dict()
for i in range(3):
    eeg = pd.DataFrame(np.random.randn(10, 2), columns=['level4_1',
        'level4_2'], index=[('level3_%s' % x) for x in range(10)])
loc, vf = 'level1_0', 'level2_0'
Why my PanelND factory throwing a KeyError?