Note that the qualifying language about plays on errors is included only in (a)(1) and not in (a)(2). First, I don't think the play from the error to the fourth ball is one continuous play since it's another pitch (or more) later. Second, the qualification simply doesn't apply.
So, credit the RBI.
Also, note that you can get RBI on balls put in play that result in errors in many situations anyway. That doesn't go to the question you asked, but it bears mentioning that just because someone makes an error doesn't mean you don't necessarily get an RBI if the situation otherwise qualifies.