Authorize.net allows you to define the number of transactions received from the same IP address within the course of an hour. The default value in the gateway is set to 10 transactions per hour. This setting, while helpful for fraud detection, does not take into account the number of transactions processed at the box office and needs to be increased.
This value should be set based on the number of transactions your organizations processes in the office per hour during peak sales times. Depending on the size of your organization this may mean 50, 100, or possible 500.