A user has all the permissions in place. An error message appears when attempting to edit related records such as Event Speaker, Event Attendee, etc.: You do not have permission to edit this record.
This error message shows up when the Event_Configuration_vod being used is configured with the Extended Object Support for the Page Layout Engine feature.
The EM Engine tries to query the Event_Layout_vod that the user should be using, receives a null response, and cannot define which Page Layout should be displayed.
This happens when the user does not have the correct Field Level Security (FLS) to the fields present on the Event_Layout_vod object for the feature.
Be sure that all the configuration steps are followed for the Extended Object Support of the Page Layout Engine feature and the end-users have the correct fields on the Event_Layout_vod object.
CRM Help Documentation: Extended Object Support for the Page Layout Engine