on two occasions now , the latest being during this game (game id no. 2181483), i have been unable to do the castling move even though neither the king or rook has moved and there is no pieces between them. Is there a rule that the castling move cannot be performed if the king is in check or is there a glitch in the system?

You can't castle when
(1) when you have moved the king or the rook that is involved in the castling, not even if the rook or king has returned to their original positions.
(2) when the king is in check or has to pass or land on a checked square.

You perform the move here at RHP by moving the king alone, two steps to the right or the left, and the rook will follow automaticly.

Thank you, i wasn't aware of the rule about the king being in check...

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