This is because the Task has been disabled. To enable the Task, navigate to
  1. Core
  2. User/Access
  3. Profile
  4. Manage Roles 
  5. Search for the All School Role
  6. Click into the All School Role Link
  7. Click Tasks
  8. Click Edit and enable the Task titled "My Groups - Master Page"​  and select both checkboxes
  9. Click Save & Exit