Are you in a group? I have never seen this but when I fly with a friend and we are in a group (with me as the one who sent out the invitation), his multiplayer options are also grayed out.
Edit: I just also found this:
Are you in a group? I have never seen this but when I fly with a friend and we are in a group (with me as the one who sent out the invitation), his multiplayer options are also grayed out.
Edit: I just also found this: