Measure won't take notes?

For some odd reason, this measure doesn't have a rest in it, and when I tried adding a note, it won't show up. Can somebody help me figure out how to fix this?

I tried adding a measure before it, copying over every note to that measure, and deleting it, but when I do, the same thing happens to the next measure; one will have nothing, not even a rest, in it, and it won't let me add anything to it, either.