If you mean Move 24, that was not an impossible move. Its a special move, like castling. Its called en passant.
Cheaters

if it was his 24th move, look at http://en.wikipedia.org/wiki/En_passant

"En passant" is another moment where I say... I love chess!! I don't have this move down yet, I haven't begun to try. It's another legal move. You can look it up under Learn. Then Special Rules. We can motivate each other to continue to work on this skill.
At one time pawns could only move one square. The idea to give them the privilege to move two squares when they start out was introduced, it is assumed, to speed up the process of the two armies getting into contact with each other. But a pawn only gets one chance to capture a pawn advancing towards it. So the en passant rule acknowledges that moving two squares is a privilege and is not meant to afford an opposing pawn the chance to sneak passed the square on which it faces capture. It does (notionally) still pass through that square and the opposing pawn can take it on that square.
How and where can I report cheaters?
My last game against ************ had an impossible move.
I really hate that when people do that!
Thanks for you help.