Hi Francois,
Thanks a lot for the update, it seems to work ! 
And thanks for the explanation. My atlas was not imported more than a year ago but maybe my freesurfer version is older.
I don’t really know what you mean with your comment about the average of the sources and the sources of the average.
The sources of my average recording file are calculated automatically, right? But you told me once that I should calculate my average source from the single trial sources. That is what I did. But I don’t see why they differ? If I open the time source of a scout they are perfectly overlaid. So it wouldn’t make a difference which one I use, but I always use the average sources based on the single trial sources.
Do I get something wrong here?
Thanks a lot
Maren