Having followed the official docs on how to set up load balancing on IIS we went for the recommended option of File Storage with File Replication.

We have 2 Win2008 R2 servers that use windows load balancing software (NLB).  Each have a copy of the umbraco site on them, with wan sync and the exclusions set up as per the documentation linked above.

The distributedCalls element in umbracoSettings.config is configured correctly as per the docs (enable=true, user=0, 2 server entries, one for each machine.

but whenever i publish content it fails, and i get the following in the logs...

2013-10-01 17:42:34,054 [12] INFO  Umbraco.Core.Publishing.PublishingStrategy - [Thread 23] Content 'testing page' with Id '1215' has been published.

2013-10-01 17:42:34,101 [12] INFO  Umbraco.Core.Sync.DefaultServerMessenger - [Thread 23] Submitting calls to distributed servers

2013-10-01 17:42:34,179 [12] ERROR Umbraco.Core.Sync.DefaultServerMessenger - [Thread 23] Error refreshing a node in the distributed list, URI attempted: http://ourserver-node1/umbraco/webservices/cacheRefresher.asmx

System.Net.WebException: The request failed with HTTP status 401: Unauthorized.

   at System.Web.Services.Protocols.SoapHttpClientProtocol.ReadResponse(SoapClientMessage message, WebResponse response, Stream responseStream, Boolean asyncCall)

   at System.Web.Services.Protocols.SoapHttpClientProtocol.EndInvoke(IAsyncResult asyncResult)

   at Umbraco.Core.Sync.DefaultServerMessenger.PerformDistributedCall(IEnumerable`1 servers, ICacheRefresher refresher, MessageType dispatchType, IEnumerable`1 ids, Type idArrayType, String jsonPayload)

There are 2 nodes configured, and i get an entry for each.  We are using the same App Pool Identity for both servers.  

From the stack trace it would seem that the user cannot be authenticated.  

I checked the machine key and it is the same for both.

Why am i still getting a 401 unauthorised?