Thank you. The full logs give a more precise location of the problem, de.lmu.ifi.dbs.elki.parallel.ParallelExecutor.run(ParallelExecutor.java:70) which makes this clearly a bug happening exactly when there is only a single core available.
It was already fixed in master (somehow I forgot that I had already discovered this): https://github.com/elki-project/elki/commit/48e82af606d4c6c133a50405a23a645391f55d80 so I can cherry-pick this change. Thank you. Regards, Erich
