Forgive me if I'm being thick here but can you only send someone a private message on here if they are actually online at the time you send it??
I thought I used to be able to message people and they'd pick them up when they logged in but I just tried to reply to someone who was online when they sent their message, but has since gone offline and my message won't send, I just get a blank screen once I press send instead of message sent.
