ds directory : /Users/yaocongd/local/Data/MEEG_2018/A1922/A1922_GlasgowFace_20190619_05.ds
    res4 data read.
    hc data read.
    Separate EEG position data file not present.
    Quaternion matching (desired vs. transformed):
       4.47   82.95    0.00 mm <->    4.47   82.95    0.00 mm (orig :  -67.80   49.75 -257.65 mm) diff =    0.000 mm
      -4.47  -82.95    0.00 mm <->   -4.47  -82.95    0.00 mm (orig :   44.38  -72.48 -266.51 mm) diff =    0.000 mm
     104.26    0.00    0.00 mm <->  104.26    0.00    0.00 mm (orig :   60.64   61.29 -243.12 mm) diff =    0.000 mm
    Coordinate transformations established.
    Polhemus data for 3 HPI coils added
    Device coordinate locations for 3 HPI coils added
---------------------------------------------------------------------------
RuntimeError                              Traceback (most recent call last)
<ipython-input-11-015f3654086c> in <module>
      2 data_path = op.join('/Users/yaocongd/local/Data/MEEG_2018/',sub);
      3 dir_list = os.listdir(data_path)
----> 4 mne.io.read_raw_ctf(op.join(data_path,dir_list[2]), system_clock='truncate', preload=True, clean_names=False, verbose=None)

~/anaconda3/envs/mne/lib/python3.6/site-packages/mne/io/ctf/ctf.py in read_raw_ctf(directory, system_clock, preload, clean_names, verbose)
     62     """
     63     return RawCTF(directory, system_clock, preload=preload,
---> 64                   clean_names=clean_names, verbose=verbose)
     65 
     66 

</Users/yaocongd/anaconda3/envs/mne/lib/python3.6/site-packages/mne/externals/decorator.py:decorator-gen-150> in __init__(self, directory, system_clock, preload, verbose, clean_names)

~/anaconda3/envs/mne/lib/python3.6/site-packages/mne/utils/_logging.py in wrapper(*args, **kwargs)
     87             with use_log_level(verbose_level):
     88                 return function(*args, **kwargs)
---> 89         return function(*args, **kwargs)
     90     return FunctionMaker.create(
     91         function, 'return decfunc(%(signature)s)',

~/anaconda3/envs/mne/lib/python3.6/site-packages/mne/io/ctf/ctf.py in __init__(self, directory, system_clock, preload, verbose, clean_names)
    115 
    116         # Compose a structure which makes fiff writing a piece of cake
--> 117         info = _compose_meas_info(res4, coils, coord_trans, eeg)
    118         info['dig'] += digs
    119         info['bads'] += _read_bad_chans(directory, info)

~/anaconda3/envs/mne/lib/python3.6/site-packages/mne/io/ctf/info.py in _compose_meas_info(res4, coils, trans, eeg)
    442         if trans['t_ctf_head_head'] is not None:
    443             info['ctf_head_t'] = trans['t_ctf_head_head']
--> 444     info['chs'] = _convert_channel_info(res4, trans, eeg is None)
    445     info['comps'] = _convert_comp_data(res4)
    446     if eeg is None:

~/anaconda3/envs/mne/lib/python3.6/site-packages/mne/io/ctf/info.py in _convert_channel_info(res4, t, use_eeg_pos)
    219             if cch['sensor_type_index'] == CTF.CTFV_REF_MAG_CH:
    220                 ch['kind'] = FIFF.FIFFV_REF_MEG_CH
--> 221                 _check_comp_ch(cch, 'Reference magnetometer')
    222                 ch['coil_type'] = FIFF.FIFFV_COIL_CTF_REF_MAG
    223                 nref += 1

~/anaconda3/envs/mne/lib/python3.6/site-packages/mne/io/ctf/info.py in _check_comp_ch(cch, kind, desired)
    138         if cch['grad_order_no'] != 0:
    139             raise RuntimeError('%s channel with non-zero compensation grade %s'
--> 140                                % (kind, cch['grad_order_no']))
    141     else:
    142         if desired is None:

RuntimeError: Reference magnetometer channel with non-zero compensation grade 1