this could be from a number of things:
often maps on the server go down- especially private maps, while the public ones just crash.
You can move your cursor over to the right hand side of the forum screen to see how many are in a map, public maps at certain hours will be full and sometimes you will receive bad tokens and failed to connects.
However if this is a private map or a low counted map- this just means the map has gone down and will be fixed once the admins reset the server.