I was one of the lucky ones who was able to log in and relocate our FC's house to a large. It did, however, take several minutes for the move to register. During that time several others attempted to purchase the plot, but could not. My FC leader also checked the board, since the relocation was taking so long. She got the option to purchase it as well, but also received the error that you mentioned. Perhaps someone had already beaten you to the house, but the server hadn't registered it yet.