Sometimes that happens but it's not because two people are booking at the same time. Once you click on the reservation time, you are the only person who's in the process of booking the reservation. The reservation will come back into the system about an hour after you get the error message.

Whenever I get an error message (which has happened for CRT more than once and many other times for other reservations...lol), the reservation always comes back an hour later and I've been able to get the reservation.