You have to download the map that you're trying to get from your own on the internet everyone has the same problem
example: I have green TD, and you don't so I enter the game and when you try to enter you will be instantly kicked so get the map before playing..
well I suggest for the admins to let people download the maps the custom maps like greentd, vamprisim speed , dotd etc :< not much of em that have that maps so too less players to have i hope it will be fixed soon,
Regards.