Hi Margot,
I modified the script bst_openmeeg.m so that it does not try to update OpenMEEG when the Brainstorm automatic updates are disabled (in the Brainstorm preferences). Update Brainstorm to get this fix.
https://github.com/brainstorm-tools/brainstorm3/commit/f60f3ea87255419abeb21a42ad1569325208d4c8#diff-9e590703ce3a61a47c365d821b1164e6
To install again an older version of OpenMEEG: delete the $HOME/.brainstorm/openmeeg folder, then use the menus Update > Update OpenMEEG > Download and Install.
Does it solve your problem?
François