There is no limit, but we have found that more errors occur with larger groups. We recommend that you register large groups in batches of 5 people at a time. Register the first five, then log out with the Login/logout link in the bottom right corner (do not use the link in the top right corner) and log back in to register. This clears the system and reduces chances of errors. Please note it may take a couple of minutes to move from screen to screen.