An error occurs when refreshing layout rules on the Event Configuration Page in CRM Online: Layout Rules Could Not Be Refreshed. Please Review Logs for More Information.
The Event Administrator may lack the Field-Level Security (FLS) read permission to the following fields on the EM_Event_Layout_vod object:
Be sure the Event Administrator has FLS read permission for all these fields mentioned above.
CRM Help Documentation: Event Layout Rules Caching