Mail Enabled Public Folders in Exchange 2010 stopped working

I recently migrated from exchange 2003 to exchange 2010.  I decomissioned my exchange 2003 server about a month ago.  Today after rebooting my exchange 2010 servers, mail enabled public folders stopped working.  I get the following kick back when I try to send an email to my mail enabled public folders:

Delivery has failed to these recipients or groups:

careers@domain.net (HumanResources@domain.net)
The e-mail system had a problem processing this message. Exchange will not try to redeliver this message for you.




Diagnostic information for administrators:

Generating server: CAS/HUB.domain.com

HumanResources@domain.net
#554 5.6.0 STOREDRV.Deliver.Exception:ObjectNotFoundException; Failed to process message due to a permanent exception with message The Active Directory user wasn't found. ##rfc822;careers@domain.net

Original message headers:

Received: from MBX.domain.com ([fe80::7439:64fd:892f:a35b]) by
 CAS/HUB.domain.com ([fe80::7060:1107:6c88:f0%10]) with mapi; Mon, 13
 Jun 2011 15:01:53 -0400
Content-Type: application/ms-tnef; name="winmail.dat"
Content-Transfer-Encoding: binary
From: "User 1" <user1@domain.net>
To: Human Resources <careers@domain.net>
Subject: test
Thread-Topic: test
Thread-Index: Acwp/FpLTT+PngphT1+puQWJloiUPQ==
Date: Mon, 13 Jun 2011 15:01:51 -0400
Message-ID: <87E33DFDC180BF44B9CE764331FC71765102B7F4@MBX.domani.com>
Accept-Language: en-US
Content-Language: en-US
X-MS-Has-Attach:
X-MS-TNEF-Correlator: <87E33DFDC180BF44B9CE764331FC71765102B7F4@MBX.domain.com>
MIME-Version: 1.0

Any ideas on what is causing this?  Thanks.