CRM 2011 email Plugin: InputParameters.Contains("Target") == false ERROR

I am trying to to implement a plugin that parses the email body from html email to text.

The problem is that for some reason

"Target") is false and the following error is thrown

01/28/2013 16:32:57 : #9628 - An error occurred while delivering the e-mail message with subject "email test " in mailbox xxx for delivery to yyy System.ServiceModel.FaultException`1[Microsoft.Xrm.Sdk.OrganizationServiceFault]:
 --------------->ERROR 2a (Fault Detail is equal to Microsoft.Xrm.Sdk.OrganizationServiceFault).

The general configuration of the plugin is:

Message: DeliverIncoming

Primary entity: email

Secondary entity:  none

Stage: pre-operation

Mode : synchronous

And the code is:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Microsoft.Xrm.Sdk;

namespace HtmlEmailToText2
{
    public class ConvertPlugin : IPlugin
    {
        public void Execute(IServiceProvider serviceProvider)
        {
            //Extract the tracing service
            ITracingService tracingService = (ITracingService)serviceProvider.GetService(typeof(ITracingService));
            if (tracingService == null)
            {
                throw new InvalidPluginExecutionException("Failed to retrieve the tracing service.");
            }

            IPluginExecutionContext pluginExecutionContext = (IPluginExecutionContext)serviceProvider.GetService(typeof(IPluginExecutionContext));

            if (pluginExecutionContext == null)
            {
                throw new InvalidPluginExecutionException("Failed to retrieve the execution context.");
            }


            Entity entity = null;

            // additional checks:
            // plug-in is not running synchronously
            // plug-in is not running against the 'Email' entity
            // plug-in is not running in the 'pre-processing' stage of the pipeline

            // e-mail handled by the e-mail router triggers the "DeliverIncoming" event
            if (pluginExecutionContext.PrimaryEntityName != "email")
            {
                throw new InvalidPluginExecutionException("-------------->ERROR 1");
            }

            if (pluginExecutionContext.InputParameters.Contains("Target") )
            {
                if (pluginExecutionContext.InputParameters["Target"] is Entity)
                {
                    // Obtain the target entity from the input parmameters.
                    entity = (Entity)pluginExecutionContext.InputParameters["Target"];
                }
                else 
                {
                    throw new InvalidPluginExecutionException("--------------->ERROR 2b");
                }
            }
            else
            {
                throw new InvalidPluginExecutionException("--------------->ERROR 2a" + pluginExecutionContext.InputParameters.Contains("Target").ToString());
            }

            try
            {
                tracingService.Trace("The plugin has started..");

                //  entity["new_textdescription"] = ConvertHtmlToText((string)entity["description"]);

                entity.Attributes["new_textdescription"] = "testing ";

             //   pluginExecutionContext.InputParameters["Target"] = entity;

                // IOrganizationServiceFactory factory = (IOrganizationServiceFactory)serviceProvider.GetService(typeof(IOrganizationServiceFactory));
                // IOrganizationService service = factory.CreateOrganizationService(pluginExecutionContext.UserId);
                // service.Create(entity);

                tracingService.Trace("The plugin has ended..");
                throw new InvalidPluginExecutionException("This is from a plugin that i have created ");
            }

            catch (Exception ex)
            {
                throw new InvalidPluginExecutionException("---------------->ERROR : ", ex);
            }
        }
    }
}

Could anybody out there explain me what i am doing wrong please.