Issues with Facebook chat?

[shaymayca1]

The chat window doesn't 'Ping" or notify me that i have a message when i chat with this one person. It works just fine for other people when in chat, just not one. It's irritating because im often in other tabs when chatting on FB. Restarted my computer, emptied cache, settings are fine. (sound is on) Any idea what the issue could be? I'm out of ideas.

[Ronnie]

I think you have accidentally click the turn off chat to that person. open the person chat window, click the top of that chat window and turn on the chat.