Can you please try this method to Delete the DN in question via the Route Plan Report;
Deleting Unassigned Directory Numbers
This section describes how to delete an unassigned directory number from the route plan report. Directory numbers get configured and removed in the Directory Number Configuration window of Cisco CallManager Administration. When a directory number gets removed from a device or a phone gets deleted, the directory number still exists in the Cisco CallManager database. To delete the directory number from the database, use the Route Plan Report window.
Good stuff! There is a bug in certain versions of CCM where the Forwarding details of a DN/Phone that has been deleted are still retained. The way to clean up this remnant info is to remove via Route Plan Report before re-using the DN.
Are you getting this error “Installer User Interface Mode Not Supported. The installer cannot run in this UI mode. To specify the interface mode, use the -i command-line option, followed by the UI mode identifier. The value UI mode identifiers...
The below trick might come handy when you have to add a new node to a cluster but you don't have or is unsure of the security password for the publisher. This procedure has been around for ages.
1) Login into the CLI of the Publisher.