Delivery has failed to these recipients or groups

Delivery has failed to these recipients or groups:

Nancy

The e-mail address you entered couldn't be found. Check the address and try resending the message. If the problem continues, please contact your helpdesk.

Diagnostic information for administrators:

Generating server: mydomain.mydomain.local

IMCEAEX-_o=mydomain_ou=Exchange+20Administrative+20Group+20+28FYDIBOHF23SPDLT+29_cn=Recipients_cn=Nancy@mydomain.com #550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found ##

Original message headers:

Received: from mydomain.mydomain.local ([fe80::14c3:f6c9:7c1a:875a%10]) by

mydomain.mydomain.local ([fe80::14c3:f6c9:7c1a:875a%10]) with mapi; Mon, 30 Jun

 2014 08:49:42 -0400

Content-Type: application/ms-tnef; name="winmail.dat"

Content-Transfer-Encoding: binary

From: Kyle <Kyle@mydomain.com>

To: Nancy

        <IMCEAEX-_o=mydomain_ou=Exchange+20Administrative+20Group+20+28FYDIBOHF23SPDLT+29_cn=Recipients_cn=Nancy@mydomain.com>

Subject:

Thread-Index: Ac+UYa/5u6vyyF6JRcOdugxp6MJXtw==

Date: Mon, 30 Jun 2014 12:49:40 +0000

Accept-Language: en-US

Content-Language: en-US

X-MS-Has-Attach:

X-Loop: Jenn@mydomain.com

X-MS-TNEF-Correlator: 9cfcba1e-7faf-4bc5-8c16-248be398ddfa

x-kse-antivirus-interceptor-info: scan successful

x-kse-antivirus-info: Clean

MIME-Version: 1.0

Message-Id: <a1a7d9db56524982be59305daccc4914@mydomain.mydomain.local>

X-KSE-Antivirus-Interceptor-Info: scan successful

X-KSE-Antivirus-Info: Clean
Other user get this response when sending to "Jenn@mydomain.com"
The recipient that the server returns saying can't be found has never been an email address.
the email address that the meeting request is sent to used to be "reception@mydomain.com" 
with a user name "Nancy" but we changed it to "Jenn@mydomain.com" 
we only get this response when sending a meeting request, can send emails with no issues