but the buffering is endless, that is the batch showing "Starting OpenMEEG" when I try to compute the head model
Please post a screen capture showing the anatomy files of your subject, and another one showing the channel file. The first steps that you report as endless should take less than a second, I suspect you selected the wrong file in the subject anatomy.
OpenMEEG correctly compute surfaces (1082, 642, 642 vertices), but the bug occurs when I try to compute the head model.
If this is the same error message as before: I already mentioned it means OpenMEEG is not installed correctly. Check where is the om_write_geom executable.