Hi Raymundo,
sorry for the late response!
Actually no, I am using process_megreg on raw files not on imported data! I want to have one head model per participant and retrieve the inverse kernel to map channels to sources.
Why should process_megreg be used only on imported data? In my opinion, it should be done on raw files rather than imported data during the processing pipeline, and it's actually like that in the tutorials: megreg before reviewing/cleaning: https://neuroimage.usc.edu/brainstorm/Tutorials/ChannelFile#Multiple_runs_and_head_positions