It doesn't matter what room you were in earlier, if you can't resolve the network server. You have to resolve the network server in order to connect to the network, which, in turn, is needed to connect to the room.
Since you say that you are able to talk to other people that are in that room, find out what the server address that they are connecting to is, then try connecting to that address using /server <server address> replacing <server address> with the actual address.
