we have a couple of user which are fully archived and the AD user was deleted but we forgot to disable archiving before deleting the AD user, so now i am not able to do this.
How can this be done that i dont get errors in the Event Log.
I am not quite sure, but a deleted user should not have a working mailbox. Also EV will not archive mailboxes without an existing aduser.
So I dont even think this step is neccessary.
Also it is recommended to build an ADgroup "deactivated Users", EV should get an exchange policy where all existing items will be archived. And no further items will be archived anymore.
This way you will not accidently delete users before changing their policies.