401: Unauthorized with NLB using CRM 2011 and counter plugin

Hi,

I have two CRM 2011 servers, let's say CRM-1 and CRM-2, with a load balance in an Azure Cloud Service.

So, after check NLB in CRM Deployment Manager, I got this exception regarding to a counter plugin

The Web Service plug-in failed in OrganizationId: adef92db-4bfc-e311-b51e-00155d891b52; SdkMessageProcessingStepId: 5f11dbb2-6203-e411-8a9b-00155d88c6c0; EntityName: incident; Stage: 10; MessageName: Create; AssemblyName: CIA.GI.Plugin.PreCreateCounter, CounterPlugin, Version=2.0.0.0, Culture=neutral, PublicKeyToken=20ee24e6e6f2faf4; ClassName: CIA.GI.Plugin.PreCreateCounter; Exception: Unhandled Exception: System.Net.WebException: The request failed with HTTP status 401: Unauthorized.
   at Microsoft.Crm.Extensibility.LegacySdkTypeProxyMetadataServiceWrapper.InternalInvoke(MethodInfo methodInfo, Object[] parameters)
   at CIA.GI.Plugin.PreCreateCounter.Execute(IPluginExecutionContext context)
   at Microsoft.Crm.Extensibility.V4PluginProxyStep.ExecuteInternal(PipelineExecutionContext context)
   at Microsoft.Crm.Extensibility.VersionedPluginProxyStepBase.Execute(PipelineExecutionContext context)

So, in CRM-1 I unregistered the .dll and register again, and worked because cold create a Incident using this plugin in CRM-1, but did the same for CRM-2 and didn't solve the problem is this server.

But, then, I realized that in CRM-1 the error come back but this time randomly, I mean I this error, but if I keep clicking Save at second or third time the record is created.

Within CRM-2 server, I can't overpass it, as in CRM-1.

If I disable the plugin step involve in the Incident creation, I don't get the exception.However I have another assembly registered and it is running fine.

Which could be the problem here?