There are different levels of infallibility, from the greater (the Manifestations who are "omniscient at will") to the lesser (like the Guardian, who has conferred freedom-from-error).
Epistemological Implications of the Gradated Claims to Divine Authority in the Bahá'í Writings:
Reflections on Infallibility
published in Journal of Bahá'í Studies
Ottawa: Association for Baha'i Studies, 2007