Piece won't go on board, even with space to fit it into
The board is almost full but I have a piece that will fit into a space. However, the game will not let me put the piece there.
I posted a photo here: http://i.imgur.com/PPy1xFp.png
When you hover a piece over the board on a usable position, you get a highlighted background, indicating the piece can be dropped there.
That's not happening here.