There is an issue in the Connectkey controllers that can cause this. The fix/Workaround is simple.
1. on the right side in the dropdown choose to Export the address book and save it.
2. Delete the addressbook on the machine
3. Import the file from step one and choose the "add to" option when prompted.
It will at this point be back to where you were and the error will no longer occur.
I may be posting in the wrong area so please let me know.
I have a 7845 scan to email address book. it let me add 22 entires and now any time you try to add a new one it says 'display name already exists', which they do not. it has the latest software 23400. rebooted several times. help?