I'm trying to learn 3-D chess by playing Parmen against the computer. I've read the tournament rules and am fairly confident I've got a good, basic understanding of the game. However, in my first game, I've quickly encountered a situation where the program is telling me I'm trying to make an illegal move which I think would be legal.
The moves so far (I'm playing white):
- a4N, Nc6N
- c4N, Nb6N
- Nb3N, Nxc4N
- d3N, N4a5B
The move I'd like to make now is
Nxa5B, but I'm alerted that it is an illegal move. Can someone explain to me why this is?