I learned something though about the definition of perfect game, though!
An error by the pitcher's team can ruin the no-hitter if the batter gets on base. But if there is an error that does not lead to a baserunner, i.e. a pop up that someone simply carelessly catches but drops it in foul territory, that kind of error is allowed for a perfect game. As long as ZERO baserunners are on the bases, the pitcher can get a perfect game.
http://en.wikipedia.org/wiki/Perfect_game
I guess a passed ball for a 3rd-strike strikeout in where the batter reaches 1st base safely disqualify the perfect game too, when I think about it.
* CalvinTy