When the new forum was created, everyone's private messages on the old forum were transferred over. However, the new forum has an arbitrary limit of 50 private messages per user. (This can be adjusted.) Who cares? Well, those that have more than 50 messages in their "Inbox" can't receive any more private messages. The solution is to delete your private messages until you are below the limit of 50. Then you may find out that someone on this forum has been trying to contact you!