Is this effecting only one character, or all of your characters? It is possible (though quite rare, unless you get DC'ed while entering an instanced dungeon) for chars to get bugged so you get "disconnected from server" when you try to connect to them. If it's only effecting a single char, send in a ticket at support.warpportal.com and the GMs will fish the char out of the void for you.
Assuming it effects all characters, we're looking at a connectivity issue:
Do you have Lowerping/WTFast running, but not connected? If you have these running, they must be connected.
Are you on a college or work network that may be blocking outgoing connections?
In the past, you also used to get this sort of behavior if you tried to use the classic client to connect to renewal, and vise versa. But I don't think the renewal client has the option to (try and fail to) connect to classic anymore, nor the classic client the option to (try and fail to) connect to renewal.