Some Error in SMS codeing

hi,

kindly find red color highlight error part.

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

using Microsoft.Xrm.Sdk;

using Microsoft.Xrm.Sdk.Query;

using Microsoft.Xrm.Sdk.Messages;

using Microsoft.Xrm.Sdk.Workflow;

using Microsoft.Crm.Sdk.Messages;

using System.Activities;

using System.Runtime.Serialization;

namespace workflow1

{

    public class class1: CodeActivity

    {

        protected override void Execute(CodeActivityContext context)

        {

            IWorkflowContext workflowcontext = context.GetExtension<IWorkflowContext>();

            IOrganizationServiceFactory servicefactory=context.GetExtension<IOrganizationServiceFactory>();

            IOrganizationService service = servicefactory.CreateOrganizationService(workflowcontext.UserId);

            Entity entity = service.Retrieve(workflowcontext.PrimaryEntityName, workflowcontext.PrimaryEntityId, new ColumnSet("new_users"));

            if (entity != null)

            {

                string name = entity.GetAttributeValue<EntityReference>("new_users").Name;

                Guid id = entity.GetAttributeValue<EntityReference>("new_users").Id;

                Entity email = new Entity("email");

                Entity Fromparty = new Entity("activityparty");

                Entity toparty = new Entity("activityparty");

                toparty["partyid"] = new EntityReference("systemuser",id);

                fromparty["partyid"] = new EntityReference("systemuser",workflowcontext.UserId);

                Guid emailid = service.Create(email);

                SendBulkMailRequest sendemailreq = new SendBulkMailRequest

                {

                    EmailId = emailid,

                    TrackingToken = "",

                    Issuesend = true

                };

                SendEmailResponse sendemailresp = (SendEmailResponse)service.Execute(sendemailreq);

            }

        }

    }

}