If your friend's forum nickname is the same to someone else's, it may have sent to that other user and not your friend. A good fix for this is changing the nickname, but you could also go to your friend's profile, click "add to buddy list," the go to the send message screen > "find members," then type would friend's forum name with "buddies only" checked. Then the message will be sent to their username. That should work for you.
As for not recieving messages, do you know if the topic was actually deleted, and you just didn't get a reply? If you know it wasn't deleted and it's been a while, you could try sending it to another MOD.
No problem. :3 Good luck.