File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/klusta/launch.py", line 250, in klusta
    model = KwikModel(kwik_path, channel_group=channel_group)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/klusta/kwik/model.py", line 593, in __init__
    clustering=clustering)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/klusta/kwik/model.py", line 1056, in open
    self._channel_group_changed(self._channel_group)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/klusta/kwik/model.py", line 1145, in _channel_group_changed
    self._load_features_masks()
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/klusta/kwik/model.py", line 795, in _load_features_masks
    fm = _mmap_h5(kwx_path, h5_path)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/klusta/kwik/h5.py", line 61, in _mmap_h5
    assert offset > 0