1017 meanings the world is full and they can not let you in. While put you in queue means there are several spaces are left in the server, therefore you can queue in for your turn but because there are people ahead of you, therefore you have to wait.

An example explanation: A world can only hold 5000 Players at any given time. So if you try to log in while the sever already has 5k players occupied, it will not let you in. Now, after a while 1000 players log off due to some various reason, means there are 1000 slots available. If you log in at this time, you will be put in queue. Say if your queue number is 378, you will get in eventually. However, the server will not accept any more player if there are already 1000 players in queue.

Not the best explanation out there but I think you can understand :P