Question:
When I have multiple users, I can view the other users calendars with an admin user. But I can’t use the admin user to add events to other users calendars. How can I change this behavior so that the admin user can add events to the other users calendars.

Solution:
In file ‘/server/html/event-create.html.php‘, there are three load options to choose from

LOAD_ALL_CALENDARS

LOAD_MY_CALENDARS

LOAD_USER_CALENDARS

Change the load option to 

LOAD_MY_CALENDARS