This message means the number of visitors on your reservation is larger than the capacity the location of the scheduled program will hold. To correct, update the capacity on the program or event, or choose a different program with the capacity to hold the group.

To update capacity of event:
  1. Click on Tickets> Program Search
  2. Search for your scheduled program and open
  3. Click Event list, and select the Event date
  4. From Event Record, underneath Tasks click Edit Event
  5. Next to Capacity, update the number and Save

If you do not want to increase the capacity on the program or event, you can instead create multiple itineraries on the reservation. Make sure your capacity for each itinerary is no more than the capacity of the program you are booking.