  We analyze MOA-2010-BLG-311, a high magnification (A_max>600) microlensing
event with complete data coverage over the peak, making it very sensitive to
planetary signals. We fit this event with both a point lens and a 2-body lens
model and find that the 2-body lens model is a better fit but with only Delta
chi^2~80. The preferred mass ratio between the lens star and its companion is
$q=10^(-3.7+/-0.1), placing the candidate companion in the planetary regime.
Despite the formal significance of the planet, we show that because of
systematics in the data the evidence for a planetary companion to the lens is
too tenuous to claim a secure detection. When combined with analyses of other
high-magnification events, this event helps empirically define the threshold
for reliable planet detection in high-magnification events, which remains an
open question.
