I think that that's what happened. On another forum I had a full PM box and at the top of the forums where is says "Private Messages: Unread 0, Total 99" I got an ALL CAPS message saying that my message box was full. Also, the admin of that forum (also main developer and CEO of the development company) never cleared his PM box so that he couldn't get any new messages, he wanted to be contacted by e-mail. So I think you'd better clean up a bit.
I was just about to say "Do you want me to send you 18 PM's and see what happens?" Probably not a good idea then.