Deleted user - uid-ghost-user still there

Hi Community!

I still run Mavericks OS X Server and as I try to update to El Capitan Server, all services are running without contacts and calendars.

I have the suspicion that a old user that I have deleted long time ago, is still there in background and causes the fault while the update process of the calendar database.

With in the reminder app there is an old reminder server group (I have renamed it to "Can not delete user") wich I can not delete. Every time I tried it, at the next start of the app, it remains. This was a shared reminder, so the UID of the deleted user is still there. So this seems to me, that there are still "parts" of the old user in the system that prevents this reminder from deleting.

Did anyone know how to safely remove any parts of the user by its uid? It seems to me that this could even solve my update problems.

Thanks in Advance!

Jerry