Intermittent Outlook Client Access by clients

We have been experiencing connectivity issues with Outlook clients to our Exchange Server 2013. These are internal clients and autodiscover is set up using a SCP setting in our AD.

If a client gets connected - then it tends to stay connected OK. We are currently using OWA as a backup and that is working fine. Email delivery internal / external is all behaving fine.

The error below is appearing very frequently since the issue was triggered.

Thanks

Paul

Source:        MSExchange CmdletLogs
Date:          08/10/2014 15:04:27
Event ID:      6
Task Category: General
Level:         Error
Keywords:      Classic
User:          N/A
Computer:      [internal-ServerName-Fully Qualified]
Description:
Cmdlet failed. Cmdlet Get-Notification, parameters {Summary=True}.
Event Xml:
<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
  <System>
    <Provider Name="MSExchange CmdletLogs" />
    <EventID Qualifiers="49152">6</EventID>
    <Level>2</Level>
    <Task>1</Task>
    <Keywords>0x80000000000000</Keywords>
    <TimeCreated SystemTime="2014-10-08T14:04:27.000000000Z" />
    <EventRecordID>12260</EventRecordID>
    <Channel>MSExchange Management</Channel>
    <Computer>[internal-ServerName-Fully Qualified]</Computer>
    <Security />
  </System>
  <EventData>
    <Data>Get-Notification</Data>
    <Data>{Summary=True}</Data>
    <Data>[Internal-AD-Name]/Users/Administrator</Data>
    <Data>S-1-5-21-3083703453-691113844-2373713632-500</Data>
    <Data>S-1-5-21-3083703453-691113844-2373713632-500</Data>
    <Data>Local-ECP-Unknown</Data>
    <Data>19664 w3wp#MSExchangeECPAppPool</Data>
    <Data>
    </Data>
    <Data>44</Data>
    <Data>00:00:00</Data>
    <Data>View Entire Forest: 'True', Configuration Domain Controller: '[internal-ServerName-Fully Qualified]', Preferred Global Catalog: '[internal-ServerName-Fully Qualified]', Preferred Domain Controllers: '{ [internal-ServerName-Fully Qualified] }'</Data>
    <Data>Microsoft.Exchange.Data.DataSourceOperationException: The request failed. The underlying connection was closed: An unexpected error occurred on a send. ---&gt; Microsoft.Exchange.WebServices.Data.ServiceRequestException: The request failed. The underlying connection was closed: An unexpected error occurred on a send. ---&gt; System.Net.WebException: The underlying connection was closed: An unexpected error occurred on a send. ---&gt; System.IO.IOException: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. ---&gt; System.Net.Sockets.SocketException: An existing connection was forcibly closed by the remote host
   at System.Net.Sockets.NetworkStream.BeginRead(Byte[] buffer, Int32 offset, Int32 size, AsyncCallback callback, Object state)
   --- End of inner exception stack trace ---
   at System.Net.TlsStream.EndWrite(IAsyncResult asyncResult)
   at System.Net.ConnectStream.WriteHeadersCallback(IAsyncResult ar)
   --- End of inner exception stack trace ---
   at System.Net.HttpWebRequest.GetResponse()
   at Microsoft.Exchange.WebServices.Data.EwsHttpWebRequest.Microsoft.Exchange.WebServices.Data.IEwsHttpWebRequest.GetResponse()
   at Microsoft.Exchange.WebServices.Data.ServiceRequestBase.GetEwsHttpWebResponse(IEwsHttpWebRequest request)
   --- End of inner exception stack trace ---
   at Microsoft.Exchange.WebServices.Data.ServiceRequestBase.GetEwsHttpWebResponse(IEwsHttpWebRequest request)
   at Microsoft.Exchange.WebServices.Data.ServiceRequestBase.ValidateAndEmitRequest(IEwsHttpWebRequest&amp; request)
   at Microsoft.Exchange.WebServices.Data.MultiResponseServiceRequest`1.Execute()
   at Microsoft.Exchange.WebServices.Data.ExchangeService.FindItems(FolderId parentFolderId, SearchFilter searchFilter, ViewBase view)
   at Microsoft.Exchange.Data.Storage.Management.EwsStoreDataProvider.InvokeServiceCall[T](Func`1 callback)
   --- End of inner exception stack trace ---
   at Microsoft.Exchange.Data.Storage.Management.EwsStoreDataProvider.InvokeServiceCall[T](Func`1 callback)
   at Microsoft.Exchange.Data.Storage.Management.EwsStoreDataProvider.&lt;InternalFindPaged&gt;d__21`1.MoveNext()
   at Microsoft.Exchange.Data.Storage.Management.AsyncOperationNotificationDataProvider.&lt;GetNotificationDetails&gt;d__4.MoveNext()
   at Microsoft.Exchange.Configuration.Tasks.GetTaskBase`1.WriteResult[T](IEnumerable`1 dataObjects)
   at Microsoft.Exchange.Management.StoreTasks.GetNotification.InternalProcessRecord()
   at Microsoft.Exchange.Configuration.Tasks.Task.ProcessRecord()</Data>
    <Data>ServerOperation</Data>
    <Data>Microsoft.Exchange.WebServices.Data.ServiceRequestException: The request failed. The underlying connection was closed: An unexpected error occurred on a send. ---&gt; System.Net.WebException: The underlying connection was closed: An unexpected error occurred on a send. ---&gt; System.IO.IOException: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. ---&gt; System.Net.Sockets.SocketException: An existing connection was forcibly closed by the remote host
   at System.Net.Sockets.NetworkStream.BeginRead(Byte[] buffer, Int32 offset, Int32 size, AsyncCallback callback, Object state)
   --- End of inner exception stack trace ---
   at System.Net.TlsStream.EndWrite(IAsyncResult asyncResult)
   at System.Net.ConnectStream.WriteHeadersCallback(IAsyncResult ar)
   --- End of inner exception stack trace ---
   at System.Net.HttpWebRequest.GetResponse()
   at Microsoft.Exchange.WebServices.Data.EwsHttpWebRequest.Microsoft.Exchange.WebServices.Data.IEwsHttpWebRequest.GetResponse()
   at Microsoft.Exchange.WebServices.Data.ServiceRequestBase.GetEwsHttpWebResponse(IEwsHttpWebRequest request)
   --- End of inner exception stack trace ---
   at Microsoft.Exchange.WebServices.Data.ServiceRequestBase.GetEwsHttpWebResponse(IEwsHttpWebRequest request)
   at Microsoft.Exchange.WebServices.Data.ServiceRequestBase.ValidateAndEmitRequest(IEwsHttpWebRequest&amp; request)
   at Microsoft.Exchange.WebServices.Data.MultiResponseServiceRequest`1.Execute()
   at Microsoft.Exchange.WebServices.Data.ExchangeService.FindItems(FolderId parentFolderId, SearchFilter searchFilter, ViewBase view)
   at Microsoft.Exchange.Data.Storage.Management.EwsStoreDataProvider.InvokeServiceCall[T](Func`1 callback)</Data>
    <Data>
    </Data>
    <Data>
    </Data>
    <Data>
    </Data>
    <Data>False</Data>
    <Data>
    </Data>
    <Data>0 objects execution has been proxied to remote server.</Data>
    <Data>
    </Data>
    <Data>
    </Data>
    <Data>0</Data>
    <Data>ActivityId: 487c8d11-0c83-40a8-8f04-2aafdddcfae5</Data>
    <Data>ServicePlan:;IsAdmin:True;</Data>
    <Data>
    </Data>
    <Data>en-GB</Data>
  </EventData>
</Event>