What does it mean when a girl is afraid to talk to you?

If you really know that the girl is afraid, and its not that she is trying to avoid you, then its because she is intimidated by you in some way. Maybe she is afraid that she will say the wrong thing and that will upset you or she is afraid you'll think she is ugly or stupid. Regardless though, it's a sign that her insecurities are taking control of her and even though she may genuinely want to talk to you, she is afraid of what you'll think of her or how you'll react to her presentation of herself.

Most of the time man, it's a good sign that you are in control there and my advice would be that you start up conversation with her. She may also be shy. Shy isn't a disease, it's just an insessive inhibition to be outgoing. She'll open up more if you take the initiatve and talk first.