title: EWS Managed: Root Element is missing
body: <p>I'm developing an Exchange Web Services Managed API client on top of ASP.NET MVC. Everything worked until we installed the latest Exchange CU update yesterday. Then I periodically got "target principal name is incorrect" errors after some time on my web server when connecting to EWS. These could get fixed temporarily by restarting the web server. </p>
  
  <p>I then used this post to configure Kerberos correctly: <a href="https://stackoverflow.com/questions/18025169/set-up-kerberos-authentication-with-delegation-on-iis-7-w-windows-server-2008">Set up Kerberos Authentication with Delegation on IIS 7 w/ Windows Server 2008</a></p>
  
  <p>Now I am stuck with the following error that I never had before: </p>
  
  <pre><code>Exception Details: System.Xml.XmlException: Root element is missing.
  [XmlException: Root element is missing.]
     System.Xml.XmlTextReaderImpl.Throw(Exception e) +88
     System.Xml.XmlTextReaderImpl.ParseDocumentContent() +1383
     System.Xml.XmlCharCheckingReader.Read() +153
     Microsoft.Exchange.WebServices.Data.EwsXmlReader.Read() +63
     Microsoft.Exchange.WebServices.Data.EwsXmlReader.Read(XmlNodeType nodeType) +44
     Microsoft.Exchange.WebServices.Data.ServiceRequestBase.ReadXmlDeclaration(EwsServiceXmlReader reader) +54
  
  [ServiceRequestException: The response received from the service didn't contain valid XML.]
     Microsoft.Exchange.WebServices.Data.ServiceRequestBase.ReadXmlDeclaration(EwsServiceXmlReader reader) +165
     Microsoft.Exchange.WebServices.Data.ServiceRequestBase.ReadSoapFault(EwsServiceXmlReader reader) +43
     Microsoft.Exchange.WebServices.Data.ServiceRequestBase.ProcessWebException(WebException webException) +413
     Microsoft.Exchange.WebServices.Data.ServiceRequestBase.GetEwsHttpWebResponse(IEwsHttpWebRequest request) +139
     Microsoft.Exchange.WebServices.Data.ServiceRequestBase.ValidateAndEmitRequest(IEwsHttpWebRequest&amp; request) +573
     Microsoft.Exchange.WebServices.Data.MultiResponseServiceRequest`1.Execute() +42
     Microsoft.Exchange.WebServices.Data.ExchangeService.FindAppointments(FolderId parentFolderId, CalendarView calendarView) +104
  </code></pre>
  
  <p>Because this is a managed version of the Exchange Web Services API I have nothing to do with the XML Requests and Responses directly. It's basically a black box for me. As you can see from the error, it occurs when calling for data from EWS. </p>