Re: Why is this a problem?
Not wrong; there are indeed orbits like you say to keep it in the sun. LADEE, however, is in a very low (50km!), circular and equatorial orbit, so it spends just under 50% of its time in the Moon's shadow - about an hour each time around.
Problem is that the batteries are designed with the assumption that they will get to charge every orbit. With a 2 (?) hour period where the moon will be much darker than usual, there's going to be at least one "charging period" that the satellite won't have the light it expects. This means the battery won't charge enough and, before it gets full sunlight again the battery will be drained "dangerously" low.
That said, normally they'd turn off many systems not necessary for the satellite's immediate survival to save power in such a case. Seems surprising to me that they can't keep it warm and alive with certainty if they turned off the science payload, for example...