I don't really get the syntax you are using, I reccognize it as shorthand and I see guys like Wilbert use it. So rather than fix it per say I rewrote it as

Code:
forward.onClick = function() {
trace (i==cards.length-1);
if (i==cards.length-1){
	i=0;
	}else{
	++i
	}
	txt2.text = cards[i][0];
	
}
and that works fine.