I was at a client with several semi-autonomous divisions and was working on enabling Free/Busy sharing between the Exchange installations at these divisions and Office 365 in preparation for their migrations. The Remote Connectivity Analyzer added a tab specifically for Office 365 that includes a Free/Busy test which can give us more information than just crossed-out availability in the Scheduling Assistant. Most of the divisions worked after being added to the Hybrid Wizard and thus the Federation and Organization Relationships configured. There were a few, however, that did not work and the RCA gave us this message when testing:

An unexpected error has occurred in the application. An event has been logged for the system administrator. If you continue to experience this error, please send us feedback.

 

Additional Details

    Exception details:

Message: Object reference not set to an instance of an object.

Type: System.NullReferenceException

Stack trace:

 

Server stack trace:

at Microsoft.Exchange.Tools.ExRca.Tests.FreeBusyPreAuthCheck.PerformTestReally()

at Microsoft.Exchange.Tools.ExRca.Tests.Test.PerformTest()

at Microsoft.Exchange.Tools.ExRca.Tests.Test.PerformChildren()

at Microsoft.Exchange.Tools.ExRca.Tests.TopLevelTest.PerformTest()

at System.Runtime.Remoting.Messaging.StackBuilderSink._PrivateProcessMessage(IntPtr md, Object[] args, Object server, Object[]& outArgs)

at System.Runtime.Remoting.Messaging.StackBuilderSink.AsyncProcessMessage(IMessage msg, IMessageSink replySink)

 

Exception rethrown at [0]:

at System.Runtime.Remoting.Proxies.RealProxy.EndInvokeHelper(Message reqMsg, Boolean bProxyCase)

at System.Runtime.Remoting.Proxies.RemotingProxy.Invoke(Object NotUsed, MessageData& msgData)

at Microsoft.Exchange.Tools.ExRca.Website.PerformTestAsyncDelegate.EndInvoke(IAsyncResult result)

at Microsoft.Exchange.Tools.ExRca.Website.TestExecutionManager.<>c__DisplayClass4.<TestCompleted>b__2()

at Microsoft.Exchange.Common.IL.ILUtil.DoTryFilterCatch(TryDelegate tryDelegate, FilterDelegate filterDelegate, CatchDelegate catchDelegate)

at Microsoft.Exchange.Tools.ExRca.Website.TestExecutionManager.TestCompleted(IAsyncResult asyncResult)

 

In every one of these cases, it was an issue with the ExternalURL on the WebServicesVirtualDirectory and/or the certificate installed on the CAS server. Some servers were missing an ExternalURL entry on the WebServices Virtual Directory. Others had what appeared to be a valid external address, but the server name in the URL was not one of the names in the SAN certificate on that server. If you see the error above, start by verifying the External URL. Make sure the URL name is in the certificate, that DNS doesn’t point that name to a different IP with a different NAT rule – check the entire connectivity stack.