  Precise instrument calibration is critical to the success of 21 cm Cosmology
experiments. Unmitigated errors in calibration contaminate the Epoch of
Reionization (EoR) signal, precluding a detection. Barry et al. 2016
characterizes one class of inherent errors that emerge from calibrating to an
incomplete sky model, however it has been unclear if errors in the sky model
affect the calibration of redundant arrays. In this paper, we show that
redundant calibration is vulnerable to errors from sky model incompleteness
even in the limit of perfect antenna positioning and identical beams. These
errors are at a level that can overwhelm the EoR signal and prevent a
detection. Finally, we suggest error mitigation strategies with implications
for the Hydrogen Epoch of Reionization Array (HERA) and the Square Kilometre
Array (SKA).
