Sim becomes invisible and only shows diamond on top

I recently saved my game and when I came back to it the female charater (who was selected at the time) became invisible. Her picture is still on the left side of the screen but when I select her to play you can't see her. This has happened once before when a couple I was playing with had a baby but this time his picture did not appear on the left side of the screen, just an outlined green box where his face should have been. When I select him to play he was also invisible. Help please!