Error on Unsuccessful Double Play Chance

Question
In the bottom of the eighth inning of yesterday's (3/31/14) game between the Cardinals and Reds, the Reds had runners at first and second with one out. Ryan Ludwick hit a grounder to second that appeared tailor-made for a 4-6-3 double play. The second baseman and shortstop executed their roles properly, recording the out at second and throwing to first. The Cardinals' first baseman, Matt Adams, however, dropped the ball, allowing Ludwick to reach and the the inning to continue with runners at the corners and two out. Adams was charged an error on the play.

While Adams clearly made a miscue on the play, I don't understand the charging of an error. This seems to me to fall under the "you can't assume a double play" rule. An out was recorded on the play, and no one took an extra base as a result of the drop. Can you explain this scoring decision?

Answer
Matty,

This is dealt with in the official rules and was scored correctly.  Here's the clause (10.12(d)3):

The official scorer shall not charge an error against any fielder who makes a wild throw in attempting to complete a double play or triple play, unless such wild throw enables any runner to advance beyond the base such runner would have reached had the throw not been wild.  However, when a fielder muffs a thrown ball that, if held, would have completed
a double play or triple play, the official scorer shall charge an error to the fielder who drops the ball and credit an assist to the fielder who made the throw.

Hope this helps!

Brian