So I logg in and click a world, and when it goes to the connecting screen it tries to connect but then says a DND blah blah is already running.. which is bogus.. how do I fix this so I can log on and play?

I wish to fix this quickly so I can play with my brother who is currently across the states.. I havent seen him in a few months because he is enlisted in the United States Marines.. and this would be a cool thing to hang out with him on.. so if anyone could help that would be amazing.