Sometimes it happens when plants fail. In fact, the plants are approximately equally divided into female and male. But when you need to grow a woman's plant, and grow a man's is no longer an order. At this choice of plants can affect anything. This is the humidity, and the temperature regime, and the light regime, if you grow in artificial conditions. BUT if the plant has become a male it can not be changed. For example, by removing male flowers. Anyway, after some time, men's flowers will appear again.
Read next
From @le0nid