Events are 'owned' by the User they are 'Assigned To', or the person who Created the Event. The insufficient privileges error that occurs is related to your Organization-Wide sharing settings and User Roles.
The video below shows how a User can Share their Calendar Events and provide Edit and Delete Access to their Calendar Events:
If a user has already been given Full Access to another user's calendar, but is still running into this error when trying to Delete an event from another user's calendar:
- The user should change the 'Related To' and 'Assigned To' fields to them-self, and Save the Event. Once the Event is Assigned To and Related To the User who is trying to Delete the Event, they are now the 'owner' of that Event and will have Delete permission for that one Event.
Users can Edit or Delete an activity or event when the following applies:
- They have the “Edit Tasks” and “Edit Events” permissions on their profile AND
- The User is Assigned To/Related To the activity, or
- The User is above the 'Assigned To' User of the activity, in the Role Hierarchy
To learn more about Role Hierarchy and creating Roles for Calendar Sharing, check out this Article: