This error can be caused by a few possibilities:
  • The group is no longer mapped to an RE group.
  • The group has been deleted. 
  • The rebuildable group includes no members.
Potential solutions to correct the issue and allow the message to send:
  1. Remove the group from the target audience and set up delivery.
  2. Set the problem group to not rebuild before delivery.
  3. Correct the issue in RE to make sure the group includes members, or it is correctly mapped to the target group in Luminate Online.