Failed to return unique result adding phone number to user or response group

When trying to add a Line URI or sip phone number to a response group.

Check for stale records in Active Directory

run command from Lync PowerShell Module

Get-CsApplicationEndpoint

And check for messages in "Yellow"

WARNING: "RegistrarPool" with identity "594603069" assigned to

"sip:1905555555@sipdomain.com" has been removed from configuration store.

Below that showed the following

Identity : CN={5bf72950-f903-4177-8887-3635a433618f},CN=Applicati

on Contacts,CN=RTC Service,CN=Services,CN=Configuratio

n,DC=Domain,DC=local

RegistrarPool : 594603069

HomeServer : CN=Lc Services\0ADEL:c5c61b5f-19a0-49a0-9aa3-e6841778f

1d1,CN=Deleted Objects,CN=Configuration,DC=Domain,DC

=local

OwnerUrn : urn:application:RGS

SipAddress :sip:1905555555@sipdomain.com
DisplayName : Company Name

DisplayNumber : +19055555555

LineURI :tel:+19055555555

PrimaryLanguage : 0

SecondaryLanguages : {}

EnterpriseVoiceEnabled : True

Enabled : True

Locate the Identity in Active Directory using ADSIEdit

And Delete the "CN" located at the end of the Identity String  ie. "CN={5bf72950-f903-4177-8887-3635a433618f}"

And try and add your Line URI or Response Group SIP Address.