It depends on what you refer to as "mistake", "wrong" and "all knowing".
For example, the first known schism  brought 5 points to discussion, 4 pertaining to arahants:
- 1: that an arahant can be seduced by another person
- 2: that an arahant may be ignorant of some matters
- 3: that an arahant may be in doubt
- 4: that an arahant may receive (be instructed by) another person
A case can be made against (2) and (3) from the suttas if the matters in question are limited to nirvana and the doctrine -- which is more than reasonable. Omniscience as "knowing everything continuously" can be refuted by the suttas as well -- the Buddha not only said he did not have that power, but he declared it was impossible for a person to have it. From that standpoint, I guess (4) would make little sense to discuss further. But (1) did not reach consensus.
EDIT: For an examination of Buddha's omniscience from the suttas, see analayo's paper on the subject.
 A.K. Warder, Indian Buddhism.