I'm on Mavericks on my iMac. Messages is not sending to a friend using Messages on her iPhone. It worked fine yesterday. I can send to her on my iPad and iPod Touch, and the messages go, AND show up in the Mac. I can see her replies on the Mac. I've tried signing in and out, deleting the preferences..nothing. Tried sending to both apple ID and the phone number...nothing Tested with another iMessage friend, same problem. AIM chat is working fine. Any one have any ideas on this?