How to restart a quest if it doesn't trigger (freeing slaves in groshoul on gallen)

liquidfire

Hi, I was in groshoul on gallen, doing the main quest on finding Cassandra, and a slave girl asked me to free her. However, when I clicked on the option to say yes, I had an error messaged saying invalid command. May I know if this a bug, otherwise, how do I trigger this quest? Thanks.