Umbraco fails to Publish! We get an exception within a load balanced environment.

After a deployment to our live servers which are load balanced we could not Publish. We could Save but not right-click publish or by clicking on the icon.

This was the error:

ERROR Umbraco.Web.UmbracoApplication - [Thread 36] An unhandled exception occurred
System.Web.HttpUnhandledException (0x80004005): Exception of type 'System.Web.HttpUnhandledException' was thrown. ---> System.TypeInitializationException: The type initializer for 'umbraco.presentation.cache.dispatcher' threw an exception. ---> System.NullReferenceException: Object reference not set to an instance of an object.
   at umbraco.presentation.cache.dispatcher..cctor()
   --- End of inner exception stack trace ---
   at umbraco.presentation.cache.dispatcher.Refresh(Guid factoryGuid, Int32 Id)
   at umbraco.library.UpdateDocumentCache(Document doc)
   at umbraco.cms.presentation.editContent.Publish(Object sender, EventArgs e)
   at System.Web.UI.WebControls.ImageButton.OnClick(ImageClickEventArgs e)
   at System.Web.UI.WebControls.ImageButton.RaisePostBackEvent(String eventArgument)
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
   at System.Web.UI.Page.HandleError(Exception e)
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
   at System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
   at System.Web.UI.Page.ProcessRequest()
   at System.Web.UI.Page.ProcessRequest(HttpContext context)
   at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
   at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

This seemed to be an error with the distributed call from server 1 to server 2 in the load balancer.

1. First I thought it might be a rewrite rule in \config\UrlRewriting.config - it wasn't
2. Then I recycled the app pools - this didn't help
3. I then made sure I could access the Umbraco web service on both servers:
1. http://serverip1/umbraco/webservices/CacheRefresher.asmx - worked
2. http://serverip2/umbraco/webservices/CacheRefresher.asmx - worked
4. I disabled distributed calls and then Publish worked, but this wasn't a solution
5. Finally the solution was due to incorrect config in \config\umbracoSettings.config. I somehow didn't have the <user>0</user> tag:

<distributedCall enable="true">

    <user>0</user>

    <servers>

      <server>serverip1</server>

      <server>serverip2</server>

    </servers>

</distributedCall>

These are some of the very useful posts I read, but config was my solution:

http://our.umbraco.org/forum/ourumb-dev-forum/bugs/3140-Type-Initialization-Error

http://our.umbraco.org/forum/ourumb-dev-forum/bugs/12909-Error-with-Publish-at-and-Distributed-calls-bad-match

https://github.com/umbraco/Umbraco-CMS/blob/4.11.7---ITask-updates/src/Umbraco.Web/umbraco.presentation/umbraco/cache/dispatcher.cs

http://stackoverflow.com/questions/19131915/umbraco-content-syncing-issue-error-refreshing-a-node-in-the-distributed-list