Users may notice this error when attempting to delete a Participant record that still has at least one guest associated with it.
1. Go to Records > Events 2. Open the Event record and click the Participants tab 3. Open the Participant record in question, and click the Guests button in the bottom right 4. Highlight the guest name and click delete 5. Repeat for all guest records attached to the Participant
Once you have removed all guests from the Participant, you will now be able to delete the Participant record.