Quoted from beelzeboob:
I sometimes get the single drop bad error message. My tech, who has a lot of experience with these machines, told me that it's common and is some kind of software glitch. It should go away almost immediately or with a restart. It did for mine. Kind of weird, but hopefully its the case with yours.
Yeah that's usually not a real error. It seems to show up if you play a game without hitting it.