Root Cause:
There are a few conditions which limit the ability to delete users and typically keeping intact a history configured for the system is reason for the limitation.Workaround:
If you track organization hierarchy, you cannot delete a user with associated hierarchy history records; so, instead, you must set that user to Inactive.
Note: If the user is assigned tasks in Task Tracking, you must reassign the tasks before you set the user to Inactive.
ArticleNumber:
000042387