Trying again, I played 1. Nc7, the robot replied with 1... Nd8 (which abandons guard of d6), so I tried to play 2. R×d6#, but the robot evoked a rejection pop-up window with "Wrong Move." Only when I keyed in 2. Rd5#, was that properly processed as successful.

What was wrong with 2. R×d6# (?) --why was it refused?? 🤪
That likely chalked up another wrong move in my stats! 😖

..................THIRD TRY
1. Nc7..., robot replied 1... d1=Q, I tried 2. Rd5#, which was approved. I can't find any other mating move there for White. It looks like the software is programmed to approve 2. Rd5 but programmed to refuse 2. R×d6 or 2. Q×d2.

I played 1. Nc7..., (robot played) Nd8.
I tried 2. Rd5#, when the rude pop-up read, "Not Quite. Try again!"
Chalk up another ding in my Wrong Moves tally, which is a total fantasy.

After 1. Nc7, (robot replied) ...Rc1, etc., then Rd1, etc. It's going through a list.

Third try, the robot replied with 1... Nh8 (?) to no avail. Since this abandons Black's guard on d6, I attempted 2. Rd6# again, hoping the robot has realized his errors, but NO!
"Not quite. Try again!" and "Wrong move. Try again!" Etc...

(in Options > Alternative Solutions) ...and found an anomaly:

Black's possible replies to 1. Nc7 have listed all the possible moves for his f7 Knight: Nd8, Nh8, Nh6, N×g5, N×e5. Of these, only the last one; clicking on 1... N×e5, it shows 2. R×d5#. But 2. R×d5# ought to be listed after ALL these possible moves for Black's f-Knight: Nd8, Nh8, Nh6, and N×g5, as well as for 1... N×e5.

Someone needs to add 2. R×d5# to those other 5 moves.

S/A = 68/417 = 16%
Added 17 years ago. 84% of participants failed to solve.
These errors have been messing up viewers all that time? 😯