Demoted Domain Controller and now Exchange 2013 keeps getting topology errors!

We recently migrated from Exchange 2007 to 2013. Everything was going good until we demoted an old domain controller. There is still a primary DC at this site. We keep getting topology and Transport errors on the Windows Server 2012 Exchange 2013 server about not being able to contact DC and Outbound Authentication failed. This happens about twice a day. A reboot of the server temporarily resolves it. Any thoughts? I have removed the name server DNS records referencing the old DC. That old DC server is still in use, but no longer as a DC. We are on CU3 version of Exchange. Thanks for any help! I have tried about everything suggestion possible online.

Errors:

MSExchange RPC Over HTTP Autoconfig Event ID: 2001

A transient failure has occurred. The problem may resolve itself in a while. The service will retry in 00:00:15. Message:
Could not find any available Domain Controller.

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MSExchangeTransportSubmission Event ID: 2017

Outbound authentication failed with error -2146892990 for Send connector Mailbox Proxy Send Connector. The authentication mechanism is ExchangeAuth. The target is SMTPSVC/exchangeserver.domain.local.

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MSExchangeADTopology Event ID: 2142

Process Microsoft.Exchange.Directory.TopologyService.exe (PID=2360) Forest domain.local. Topology discovery failed, error details 
Active Directory server  is not available. Error message: Active directory response: A local error occurred..

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MSExchange Front End HTTP Proxy Event ID: 3002

[RpcHttp] Failed to refresh ClientAccess 2010 server map. The exception was: Microsoft.Exchange.Data.Directory.NoSuitableServerFoundException: The Microsoft Exchange Active Directory Topology service on server localhost did not return any suitable domain controllers for forest BuchananGroup.local.
   at Microsoft.Exchange.Data.Directory.ServiceTopologyProvider.GetConfigDCInfo(String partitionFqdn, Boolean throwOnFailure)
   at Microsoft.Exchange.Data.Directory.TopologyProvider.PopulateConfigNamingContexts(String partitionFqdn)
   at Microsoft.Exchange.Data.Directory.TopologyProvider.GetConfigurationNamingContext(String partitionFqdn)
   at Microsoft.Exchange.Data.Directory.ADSession.GetConfigurationNamingContext(String partitionFqdn)
   at Microsoft.Exchange.Data.Directory.ADDataSession.GetNamingContext(ADNamingContext adNamingContext)
   at Microsoft.Exchange.Data.Directory.ADDataSession.GetConnection(String preferredServer, Boolean isWriteOperation, String optionalBaseDN, ADObjectId& rootId, ADScope scope)
   at Microsoft.Exchange.Data.Directory.ADDataSession.GetReadConnection(String preferredServer, String optionalBaseDN, ADObjectId& rootId, ADRawEntry scopeDeteriminingObject, DualSearchMode dualSearchMode)
   at Microsoft.Exchange.Data.Directory.ADGenericReader.GetNextResultCollection(Type controlType, DirectoryControl& responseControl)
   at Microsoft.Exchange.Data.Directory.ADPagedReader`1.GetNextResultCollection()
   at Microsoft.Exchange.Data.Directory.ADGenericPagedReader`1.GetNextPage()
   at Microsoft.Exchange.Data.Directory.ADGenericPagedReader`1.<GetEnumerator>d__0.MoveNext()
   at Microsoft.Exchange.Data.Directory.ADGenericPagedReader`1.ReadAllPages()
   at Microsoft.Exchange.HttpProxy.DownLevelServerManager.InternalRefresh()