This position doesn't meet one of the requirements for castling:
Unattacked: All of the squares between the king's initial and final squares (including the initial and final squares) must not be under attack by any opposing piece.
(hide) If you are waiting for your turn, click on "change" next to the "refresh" on the main page, then set refresh the page to 30 seconds to get your turn to move displayed faster. (Servant) (show all tips)