Hi Jamie,
Please try to use this method to completely remove this DN before trying again.
**Remove this DN from all phones first;
Can you please try this method 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.
Procedure
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Step 1 Choose Route Plan > Route Plan Report.
The Route Plan Report window displays. Use the three drop-down list boxes to specify a route plan report that lists all unassigned DNs.
Step 2 Three ways exist to delete directory numbers:
a. Click the directory number that you want to delete. When the Directory Number Configuration window displays, click Delete.
b. Check the check box next to the directory number that you want to delete. Click Delete Selected.
c. To delete all found unassigned directory numbers, click Delete all Found Items.
A warning message verifies that you want to delete the directory number.
Step 3 To delete the directory number, click OK. To cancel the delete request, click Cancel.
From this good doc;
http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_administration_guide_chapter09186a00803ed686.html#wp1024696
Hope this helps!
Rob
