I have never used Multiplayer Trainz but I suspect that that command is used to send a train from your portal to a portal in the same session used by another player (the user) in a multiplayer game. Since no other player is logged on to your game (or however it works), there is "NOBODY" to send the train to. That is my theory anyway.
Is the session you are using identified as "Multiplayer" or "MP"? (but not all of them identify themselves this way)