This is likely because the event is Secure but no roles have been granted access.

To verify this: 
  1. Navigate to School Website > Content > Events
  2. Select the gear to edit the event settings next to the event in question.
  3. Under Access check to see if the event is marked a Public or Secure
  4. If the event is public, it can be viewed by anyone. If the event is secure, only select roles will have access.
  5. If the event is secure, make sure that the correct roles are selected.

User-added image

Note: If no roles have been selected, no users will be able to view the event.. This includes Parents and School Faculty/Staff.