cannot create an abstract class

Question

I'am adding a new method to my SOAP WS,but i'am getting the error "cannot create an abstract class" when testing with soapUI.

 [DataContract(Namespace = Configuration.Namespace)]
public  class DemandeAutomatique
{
    #region Champs
    [DataMember(Name = "Titre")]
    public string title { get; set; }

    [DataMember(Name = "NumeroDemande")]
    public string ticketnumber { get; set; }

    [DataMember(Name = "GUIDDemande")]
    public Guid? incidentid { get; set; }


}

Interface :

 [OperationContract]
    [FaultContract(typeof(ServiceFault))]
    CreateDemandeResponse NotifyForCreate(DemandeAutomatique demande);

Implementation :

  public class ManageDemandeService : IManageDemandeService { CreateDemandeResponse IManageDemandeService.NotifyForCreate(DemandeAutomatique  demande)
{
    ValidationWSDL.NotifyForCreate(ref _log, demande);
    using (service = CrmServiceFactory.GetOrganizationServiceProxy())
    {
        req=
        if (service != null)
       OrganizationRequest Req = new OrganizationRequest("DemandeWS");
         Req["Demande"] = dmd;try
            { OrganizationResponse response = service.Execute(Req);
                return new CreateDemandeResponse() { GUIDDemande = Guid.Parse(response.Results["GUIDDemande"].ToString()) };
            }
            catch (System.ServiceModel.FaultException<OrganizationServiceFault> crmFault)
            {
      throw new FaultException(new ServiceFault("Erreur lors du traitement plugin. " + crmFault.Detail.Message, crmFault.Detail, ServiceFault.ErreurOrganizationServiceFaultCode));
            }
        }}
}
}