The "took too long to login" thing is because you need to sign in to the server to confirm your account, but it's timing out because of the server being overloaded. Monsters have nothing to do with it.
You could solve this by turning online-mode to false, which stops it from confirming identities but that lets people spoof names and other dumb stuff.
Or just wait like half an hour or so for the activity to die down a bit.