Hey,
Don't being worried, the server say "there is already someone connected" but it's because you was logged when Citadel stopped and your character "stayed" in the server, I tried to connect with my other accounts and I could reach the characters page but couldn't connect, the problem is just from the Citadel server, they got ddos or crashed or something other like maintenance maybe ^-^/
We just have to wait they restart the servers :3