Got this error for one of  our supported Exchange 2013 environments, outlook.proxy healthset showed alert state; got the same error when I ran the probe on another box whose healthset showed as healthy.

Questions:

What does unknown app pool mean? how to fix it?

Why the other server is not affected by this probe and its state is still healthy? I checked there was no monitor override for this healthset. This healthset has only 1 probe.

[PS] C:\Windows\system32>Get-MonitoringItemIdentity -Identity outlook.proxy -server <servername>|select name, itemtype

Name                                                                                                           ItemType
----                                                                                                           --------
OutlookProxyTestProbe                                                                                             Probe
OutlookProxyTestMonitor                                                                                         Monitor
OutlookProxyTestRecycleAppPool                                                                                Responder
OutlookProxyTestOffline                                                                                       Responder
OutlookProxyTestOfflineFailedEscalate                                                                         Responder
OutlookProxyTestEscalate                                                                                      Responder

[PS] C:\Windows\system32>Invoke-MonitoringProbe -Identity Outlook.Proxy\OutlookProxyTestProbe -server <servername>|fl
Creating a new session for implicit remoting of "Invoke-MonitoringProbe" command...

RunspaceId         : 9e2a7e07-e833-43d1-8367-2da128ba83e0
Server             : <servername>
MonitorIdentity    : Outlook.Proxy\OutlookProxyTestProbe
RequestId          : e24b770d-47c0-4c23-b028-2824141a7131
ExecutionStartTime : 5/1/2014 2:08:38 AM
ExecutionEndTime   : 5/1/2014 2:08:38 AM
Error              : Unknown app pool name:
Exception          : System.InvalidOperationException: Unknown app pool name:
                        at Microsoft.Exchange.Monitoring.ActiveMonitoring.ClientAccess.CafeProtocols.Get(String
                     appPool)
                        at Microsoft.Exchange.Monitoring.ActiveMonitoring.ClientAccess.CafeLocalProbe.DoWork(Cancellati
                     onToken cancellationToken)
                        at Microsoft.Office.Datacenter.WorkerTaskFramework.WorkItem.Execute(CancellationToken
                     joinedToken)
                        at
                     Microsoft.Office.Datacenter.WorkerTaskFramework.WorkItem.<>c__DisplayClass2.<StartExecuting>b__0()
                        at System.Threading.Tasks.Task.Execute()
PoisonedCount      : 0
ExecutionId        : 25463867
SampleValue        : 0
ExecutionContext   : probe defined timeout=60000ms, actual timeout=60000ms, http request timeout=59000ms

FailureContext     :
ExtensionXml       :
ResultType         : Failed
RetryCount         : 0
ResultName         : e24b770d47c04c23b0282824141a7131-OutlookProxyTestProbe
IsNotified         : False
ResultId           : 11678198
ServiceName        : InvokeNow
StateAttribute1    :
StateAttribute2    :
StateAttribute3    :
StateAttribute4    :
StateAttribute5    :
StateAttribute6    : 0
StateAttribute7    : 0
StateAttribute8    : 0
StateAttribute9    : 0
StateAttribute10   : 0
StateAttribute11   :
StateAttribute12   :
StateAttribute13   :
StateAttribute14   :
StateAttribute15   :
StateAttribute16   : 0
StateAttribute17   : 0
StateAttribute18   : 0
StateAttribute19   : 0
StateAttribute20   : 0
StateAttribute21   :
StateAttribute22   :
StateAttribute23   :
StateAttribute24   :
StateAttribute25   :
Identity           : b508b529bed3427a9ad7af1e6b64ad02
IsValid            : True
ObjectState        : New

Hi Jack, did you ever get a solution for this?

I have the same thing for Autodiscover.Proxy\AutodiscoverProxyTestProbe.

Did you ever find a solution?