error while computing source space connectivity

Dear MNE experts,

I am a MEG beginner. I just started to calculate source space connectivity using the following scripts from the MNE website:

http://martinos.org/mne/stable/auto_examples/connectivity/plot_mne_inverse_label_connectivity.html#sphx-glr-auto-examples-co

I downloaded the .py file and made some modifications according to my MEG data. I succeeded with loading the raw, events and the inverse_operator files. The picks and epochs also seem to be correct. However, when I tried to calculate connectivity (using the spectral_connectivity function), I got the following error message:

/usr/pubsw/packages/python/anaconda/lib/python2.7/site-packages/mne/connectivity/spectral.pyc in spectral_connectivity(data, method, indices, sfreq, mode, fmin, fmax, fskip, faverage, tmin, tmax, mt_bandwidth, mt_adaptive, mt_low_bias, cwt_frequencies, cwt_n_cycles, block_size, n_jobs, verbose)
    769 if epoch_idx == 0:
    770 # initialize everything
--> 771 first_epoch = epoch_block[0]
    772
    773 # get the data size and time scale

IndexError: list index out of range

I checked the label_ts variable, it seems like this:

<generator object _gen_extract_label_time_course at 0x2ba48c651a00>

So could someone please help me with this problem?

Best wishes,
Baojuan
<http://martinos.org/mne/stable/generated/mne.connectivity.spectral_connectivity.html#mne.connectivity.spectral_connectivity>
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