I just went off EMC like a minute ago and now can't get back on any servers.. just says "Failed to login: Bad login" I restarted my minecraft but that didn't help..
That can mean that someone is using your MC account - not on EMC but for single player or on other servers. Change your MC password.
You can also play on somebody other's account without knowing his or her password. I once logged in as a server owner somewhere, without knowing his password.