  We analyze PLANET and MACHO observations of MACHO 99-BLG-47, the first
nearly-normal microlensing event for which high signal-to-noise-ratio data
reveal a well-covered, short-duration anomaly. This anomaly occurs near the the
peak of the event. Short-duration anomalies near the peak of otherwise normal
events are expected to arise both from extreme-separation (either very close or
very wide), roughly equal-mass binary lenses, and from planetary systems. We
show that the lens of MACHO 99-BLG-47 is in fact an extreme-separation binary,
not a planetary system, thus demonstrating for the first time that these two
important classes of events can be distinguished in practice. However, we find
that the wide-binary and close-binary lens solutions fit the data equally well,
and cannot be distinguished even at Delta-chi^2=1. This degeneracy is
qualitatively much more severe than the one identified for MACHO 98-SMC-1
because the present degeneracy spans two rather than one dimension in the
magnification field and does not require significantly different blending
fractions. In the appendix, we explore this result, and show that it is related
to the symmetry in the lens equation.
