From the little I've read of this case (just this thread), it's possible there was no "error of law," and even if there was, the standard for overturning a lower court is "tougher" than the standard used by the lower court.
See Reversing a Conviction - FindLaw for a little bit more.
Tough as it is to get, this remedy is easier to get from a trial court than from an appellate court.
The remedy of jury reversal only goes one way, no judge can reverse a not guilty verdict.
Thank God for that.