[ mne_volume_source_space --mri ] "no nonzero elements"

Hi All!
I am trying to produce a nifti file from MEG output as a practice to get
my feet wet. I am starting with the run_meg_volume_tutorial.sh
<https://github.com/mne-tools/mne-scripts/blob/master/sample-data/run_meg_volume_tutorial.sh>
but mne_volume_source_space fails when using the--mri option
...
3757 sources remaining after excluding the sources outside the surface
and less than 5.0 mm inside.
Adjusting the neighborhood info...[done]
Reading /home/foranw/src/MNE-sample-data/subjects/sample/mri/T1.mgz...[done]
Setting up interpolation...No nonzero elements specified.

I run into the same error trying to use local MEG (not sample) data as well.

Am I missing a step?

Thanks
Will

working:
        mne_volume_source_space --grid 7 \
          --bem
/home/foranw/src/MNE-sample-data/subjects/sample/bem/sample-5120-bem.fif \
          --src
/home/foranw/src/MNE-sample-data/subjects/sample/bem/volume-7mm-src.fif

$?==1, no output:
        mne_volume_source_space --grid 7 \
          --bem
/home/foranw/src/MNE-sample-data/subjects/sample/bem/sample-5120-bem.fif \
          --src
/home/foranw/src/MNE-sample-data/subjects/sample/bem/volume-7mm-src.fif \
          --mri /home/foranw/src/MNE-sample-data/subjects/sample/mri/T1.mgz
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