"Unrecognized function or variable 'om_write_geom'.
This error message indicates that OpenMEEG is not installed correctly, the executable om_write_geom is missing. Delete the folder $HOME/.brainstorm/openmeeg, and let Brainstorm re-install it automatically when running the computation.
but then the buffering is endless
What do you call "buffering"? The function om_write_geom is called at the beginning of the OpenMEEG computation (bst_openmeeg.m). Before that, it only saves the anatomy and dipoles in the folder $HOME/.brainstorm/tmp/. If this takes time, there is a problem, make sure you haven't selected the high resolution cortex surface in the subject anatomy.